Thanks! It works for me. With the trick I can print the numeric expression.
El sábado, 22 de junio de 2013 05:55:16 UTC+2, Aaron Meurer escribió:
>
> On Fri, Jun 21, 2013 at 5:48 PM, peibol <pab...@gmail.com <javascript:>>
> wrote:
> > Hi all
> >
> > I've been searching just to check if what I want to do is feasible with
> > sympy. The thing is that I have an expression ('a/b+c/d') for which I
> want
> > to give several sets of values and for each set render the latex without
> > evaluating it. I don't know how to avoid automatic evaluation and
> > simplification. Any help would be fantastic!
> >
> > a,b,c,d = symbols('a b c d')
> > fvars = [a,b,c,d]
> > values = [1,4,2,4]; #example: 1/4+2/4
> > exp=sympify('a/b + c/d'); #here I define the algebraic expression
> > res=nsimplify(exp.evalf(subs = dict(zip(fvars,values)))) #here I
> get
> > the result for later use
>
> Why don't you just use subs here? Are your typical values floats
> rather than ints?
>
> >
> > straux=urllib.quote(printing.latex(exp)) #urllib is for making the
> > expression URL friendly... the thing us that latex(exp)
> > #I have
> tried
> > exp.subs(a,1...) and eval (making a=1, b=4... and it gives 3/4, not 1/4
> +
> > 2/4
> >
> > strchart='
> http://chart.apis.google.com/chart?cht=tx&chs=140x50&chf=bg,s,FFFFFF00&chl='
>
> > + straux
> >
> > Thanks!
>
> The classical way to get these expressions to not evaluate is to use
> Add(evaluate=False). If all you care about is printing, you can use
> this trick
>
> In [25]: (a/b + c/d).subs([(var, Symbol("%s" % i)) for var, i in
> zip(fvars, values)])
> Out[25]:
> 1 2
> ─ + ─
> 4 4
>
> In other words, use a Symbol with the name of the function you want.
> Unfortunately, this still won't preserve the input order, which is
> currently impossible to do. I think for printing, though, otherwise
> identical expressions are sorted alphabetically (more or less), so if
> this is an issue, you could find a reliable pattern, and use the
> symbol_names argument to latex(). You could also just use symbol_names
> in the first place, instead of creating Symbol('1').
>
> Aaron Meurer
>
> >
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