Mathematica parser error ,bug ?

[Lee Philip]

test code here, error encountered there .

http://codepad.org/hZEmO4Po

what I want to do here is just convert it to a Python acceptable expression ,is there an easy way ?

[Francesco Bonazzi]

The regex parser fails to recognize in expressions such as 1/(4x-1), that 4x is 4 times x.

I tried to call M("1/(4x - 1)") and I got the following transformation:

Integer (1 )/(Integer (4 )Symbol ('x' )-Integer (1 ))

Obviously, Integer(4) Symbol('x') is not valid, as an asterisk (*) is missing to represent the multiplication.

A quick makeshift fix:

your_mathematica_expr = '((-2x+5)(4x-1)-4(-x^2+5x+1))/(4x-1)^2'
new_math_expr = re.sub("([0-9])\ *([a-zA-Z])", "\\1 * \\2", your_mathematica_expr)
M(new_math_expr)

[Francesco Bonazzi]

On Thursday, November 27, 2014 2:28:11 PM UTC+1, Francesco Bonazzi wrote:

your_mathematica_expr = '((-2x+5)(4x-1)-4(-x^2+5x+1))/(4x-1)^2'
new_math_expr = re.sub("([0-9])\ *([a-zA-Z])", "\\1 * \\2", your_mathematica_expr)
M(new_math_expr)

Remember import re to use the re module.

[Richard Fateman]

Does sympy really spell simplify  without the L?

[Richard Fateman]

answering my own question ... oh

it is creating a sympy object, not simplifying.

Sorry for the noise.

'RJF

[redstone-cold]

thanks for your kind help ! then it is surely a bug of the parser.

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[Lee Philip]

I reported the bug here https://github.com/sympy/sympy/issues/8535

在 2014年11月27日星期四UTC+8下午8时42分53秒，Lee Philip写道：

[Francesco Bonazzi]

It would be nice to use this:

https://github.com/mattpap/mathematica-parser/blob/cc38fd2aed8debfe0e4f08453d8f24b70784c494/src/main/scala/MathematicaParser.scala

Unfortunately, being written in Scala, it's really hard to include it into Python.

Anyways, the precedence operators are very clear:
https://github.com/mattpap/mathematica-parser/blob/cc38fd2aed8debfe0e4f08453d8f24b70784c494/src/main/scala/MathematicaParser.scala#L82