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340 lines
12 KiB
340 lines
12 KiB
5 months ago
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"""
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Javascript code printer
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The JavascriptCodePrinter converts single SymPy expressions into single
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Javascript expressions, using the functions defined in the Javascript
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Math object where possible.
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"""
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from __future__ import annotations
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from typing import Any
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from sympy.core import S
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from sympy.core.numbers import equal_valued
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from sympy.printing.codeprinter import CodePrinter
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from sympy.printing.precedence import precedence, PRECEDENCE
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# dictionary mapping SymPy function to (argument_conditions, Javascript_function).
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# Used in JavascriptCodePrinter._print_Function(self)
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known_functions = {
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'Abs': 'Math.abs',
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'acos': 'Math.acos',
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'acosh': 'Math.acosh',
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'asin': 'Math.asin',
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'asinh': 'Math.asinh',
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'atan': 'Math.atan',
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'atan2': 'Math.atan2',
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'atanh': 'Math.atanh',
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'ceiling': 'Math.ceil',
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'cos': 'Math.cos',
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'cosh': 'Math.cosh',
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'exp': 'Math.exp',
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'floor': 'Math.floor',
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'log': 'Math.log',
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'Max': 'Math.max',
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'Min': 'Math.min',
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'sign': 'Math.sign',
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'sin': 'Math.sin',
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'sinh': 'Math.sinh',
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'tan': 'Math.tan',
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'tanh': 'Math.tanh',
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}
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class JavascriptCodePrinter(CodePrinter):
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""""A Printer to convert Python expressions to strings of JavaScript code
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"""
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printmethod = '_javascript'
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language = 'JavaScript'
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_default_settings: dict[str, Any] = {
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'order': None,
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'full_prec': 'auto',
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'precision': 17,
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'user_functions': {},
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'human': True,
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'allow_unknown_functions': False,
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'contract': True,
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}
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def __init__(self, settings={}):
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CodePrinter.__init__(self, settings)
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self.known_functions = dict(known_functions)
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userfuncs = settings.get('user_functions', {})
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self.known_functions.update(userfuncs)
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def _rate_index_position(self, p):
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return p*5
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def _get_statement(self, codestring):
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return "%s;" % codestring
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def _get_comment(self, text):
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return "// {}".format(text)
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def _declare_number_const(self, name, value):
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return "var {} = {};".format(name, value.evalf(self._settings['precision']))
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def _format_code(self, lines):
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return self.indent_code(lines)
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def _traverse_matrix_indices(self, mat):
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rows, cols = mat.shape
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return ((i, j) for i in range(rows) for j in range(cols))
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def _get_loop_opening_ending(self, indices):
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open_lines = []
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close_lines = []
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loopstart = "for (var %(varble)s=%(start)s; %(varble)s<%(end)s; %(varble)s++){"
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for i in indices:
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# Javascript arrays start at 0 and end at dimension-1
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open_lines.append(loopstart % {
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'varble': self._print(i.label),
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'start': self._print(i.lower),
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'end': self._print(i.upper + 1)})
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close_lines.append("}")
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return open_lines, close_lines
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def _print_Pow(self, expr):
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PREC = precedence(expr)
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if equal_valued(expr.exp, -1):
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return '1/%s' % (self.parenthesize(expr.base, PREC))
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elif equal_valued(expr.exp, 0.5):
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return 'Math.sqrt(%s)' % self._print(expr.base)
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elif expr.exp == S.One/3:
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return 'Math.cbrt(%s)' % self._print(expr.base)
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else:
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return 'Math.pow(%s, %s)' % (self._print(expr.base),
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self._print(expr.exp))
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def _print_Rational(self, expr):
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p, q = int(expr.p), int(expr.q)
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return '%d/%d' % (p, q)
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def _print_Mod(self, expr):
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num, den = expr.args
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PREC = precedence(expr)
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snum, sden = [self.parenthesize(arg, PREC) for arg in expr.args]
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# % is remainder (same sign as numerator), not modulo (same sign as
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# denominator), in js. Hence, % only works as modulo if both numbers
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# have the same sign
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if (num.is_nonnegative and den.is_nonnegative or
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num.is_nonpositive and den.is_nonpositive):
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return f"{snum} % {sden}"
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return f"(({snum} % {sden}) + {sden}) % {sden}"
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def _print_Relational(self, expr):
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lhs_code = self._print(expr.lhs)
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rhs_code = self._print(expr.rhs)
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op = expr.rel_op
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return "{} {} {}".format(lhs_code, op, rhs_code)
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def _print_Indexed(self, expr):
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# calculate index for 1d array
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dims = expr.shape
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elem = S.Zero
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offset = S.One
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for i in reversed(range(expr.rank)):
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elem += expr.indices[i]*offset
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offset *= dims[i]
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return "%s[%s]" % (self._print(expr.base.label), self._print(elem))
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def _print_Idx(self, expr):
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return self._print(expr.label)
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def _print_Exp1(self, expr):
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return "Math.E"
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def _print_Pi(self, expr):
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return 'Math.PI'
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def _print_Infinity(self, expr):
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return 'Number.POSITIVE_INFINITY'
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def _print_NegativeInfinity(self, expr):
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return 'Number.NEGATIVE_INFINITY'
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def _print_Piecewise(self, expr):
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from sympy.codegen.ast import Assignment
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if expr.args[-1].cond != True:
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# We need the last conditional to be a True, otherwise the resulting
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# function may not return a result.
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raise ValueError("All Piecewise expressions must contain an "
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"(expr, True) statement to be used as a default "
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"condition. Without one, the generated "
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"expression may not evaluate to anything under "
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"some condition.")
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lines = []
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if expr.has(Assignment):
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for i, (e, c) in enumerate(expr.args):
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if i == 0:
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lines.append("if (%s) {" % self._print(c))
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elif i == len(expr.args) - 1 and c == True:
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lines.append("else {")
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else:
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lines.append("else if (%s) {" % self._print(c))
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code0 = self._print(e)
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lines.append(code0)
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lines.append("}")
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return "\n".join(lines)
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else:
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# The piecewise was used in an expression, need to do inline
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# operators. This has the downside that inline operators will
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# not work for statements that span multiple lines (Matrix or
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# Indexed expressions).
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ecpairs = ["((%s) ? (\n%s\n)\n" % (self._print(c), self._print(e))
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for e, c in expr.args[:-1]]
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last_line = ": (\n%s\n)" % self._print(expr.args[-1].expr)
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return ": ".join(ecpairs) + last_line + " ".join([")"*len(ecpairs)])
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def _print_MatrixElement(self, expr):
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return "{}[{}]".format(self.parenthesize(expr.parent,
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PRECEDENCE["Atom"], strict=True),
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expr.j + expr.i*expr.parent.shape[1])
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def indent_code(self, code):
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"""Accepts a string of code or a list of code lines"""
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if isinstance(code, str):
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code_lines = self.indent_code(code.splitlines(True))
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return ''.join(code_lines)
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tab = " "
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inc_token = ('{', '(', '{\n', '(\n')
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dec_token = ('}', ')')
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code = [ line.lstrip(' \t') for line in code ]
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increase = [ int(any(map(line.endswith, inc_token))) for line in code ]
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decrease = [ int(any(map(line.startswith, dec_token)))
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for line in code ]
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pretty = []
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level = 0
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for n, line in enumerate(code):
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if line in ('', '\n'):
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pretty.append(line)
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continue
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level -= decrease[n]
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pretty.append("%s%s" % (tab*level, line))
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level += increase[n]
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return pretty
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def jscode(expr, assign_to=None, **settings):
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"""Converts an expr to a string of javascript code
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Parameters
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==========
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expr : Expr
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A SymPy expression to be converted.
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assign_to : optional
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When given, the argument is used as the name of the variable to which
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the expression is assigned. Can be a string, ``Symbol``,
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``MatrixSymbol``, or ``Indexed`` type. This is helpful in case of
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line-wrapping, or for expressions that generate multi-line statements.
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precision : integer, optional
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The precision for numbers such as pi [default=15].
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user_functions : dict, optional
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A dictionary where keys are ``FunctionClass`` instances and values are
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their string representations. Alternatively, the dictionary value can
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be a list of tuples i.e. [(argument_test, js_function_string)]. See
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below for examples.
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human : bool, optional
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If True, the result is a single string that may contain some constant
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declarations for the number symbols. If False, the same information is
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returned in a tuple of (symbols_to_declare, not_supported_functions,
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code_text). [default=True].
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contract: bool, optional
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If True, ``Indexed`` instances are assumed to obey tensor contraction
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rules and the corresponding nested loops over indices are generated.
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Setting contract=False will not generate loops, instead the user is
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responsible to provide values for the indices in the code.
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[default=True].
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Examples
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========
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>>> from sympy import jscode, symbols, Rational, sin, ceiling, Abs
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>>> x, tau = symbols("x, tau")
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>>> jscode((2*tau)**Rational(7, 2))
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'8*Math.sqrt(2)*Math.pow(tau, 7/2)'
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>>> jscode(sin(x), assign_to="s")
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's = Math.sin(x);'
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Custom printing can be defined for certain types by passing a dictionary of
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"type" : "function" to the ``user_functions`` kwarg. Alternatively, the
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dictionary value can be a list of tuples i.e. [(argument_test,
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js_function_string)].
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>>> custom_functions = {
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... "ceiling": "CEIL",
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... "Abs": [(lambda x: not x.is_integer, "fabs"),
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... (lambda x: x.is_integer, "ABS")]
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... }
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>>> jscode(Abs(x) + ceiling(x), user_functions=custom_functions)
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'fabs(x) + CEIL(x)'
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``Piecewise`` expressions are converted into conditionals. If an
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``assign_to`` variable is provided an if statement is created, otherwise
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the ternary operator is used. Note that if the ``Piecewise`` lacks a
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default term, represented by ``(expr, True)`` then an error will be thrown.
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This is to prevent generating an expression that may not evaluate to
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anything.
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>>> from sympy import Piecewise
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>>> expr = Piecewise((x + 1, x > 0), (x, True))
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>>> print(jscode(expr, tau))
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if (x > 0) {
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tau = x + 1;
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}
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else {
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tau = x;
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}
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Support for loops is provided through ``Indexed`` types. With
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``contract=True`` these expressions will be turned into loops, whereas
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``contract=False`` will just print the assignment expression that should be
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looped over:
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>>> from sympy import Eq, IndexedBase, Idx
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>>> len_y = 5
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>>> y = IndexedBase('y', shape=(len_y,))
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>>> t = IndexedBase('t', shape=(len_y,))
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>>> Dy = IndexedBase('Dy', shape=(len_y-1,))
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>>> i = Idx('i', len_y-1)
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>>> e=Eq(Dy[i], (y[i+1]-y[i])/(t[i+1]-t[i]))
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>>> jscode(e.rhs, assign_to=e.lhs, contract=False)
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'Dy[i] = (y[i + 1] - y[i])/(t[i + 1] - t[i]);'
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Matrices are also supported, but a ``MatrixSymbol`` of the same dimensions
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must be provided to ``assign_to``. Note that any expression that can be
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generated normally can also exist inside a Matrix:
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>>> from sympy import Matrix, MatrixSymbol
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>>> mat = Matrix([x**2, Piecewise((x + 1, x > 0), (x, True)), sin(x)])
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>>> A = MatrixSymbol('A', 3, 1)
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>>> print(jscode(mat, A))
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A[0] = Math.pow(x, 2);
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if (x > 0) {
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A[1] = x + 1;
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}
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else {
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A[1] = x;
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}
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A[2] = Math.sin(x);
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"""
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return JavascriptCodePrinter(settings).doprint(expr, assign_to)
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def print_jscode(expr, **settings):
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"""Prints the Javascript representation of the given expression.
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See jscode for the meaning of the optional arguments.
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"""
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print(jscode(expr, **settings))
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