Thank you so much for your help!!! On Oct 15, 11:33 pm, Ondrej Certik <[email protected]> wrote: > On Fri, Oct 15, 2010 at 8:48 PM, HappyMac <[email protected]> wrote: > > Dear all, > > > I am new to SymPy and trying to learning how to use. > > I have installed the latest SymPy (v. 0.6.7) and tried the following > > Python script: > > > sympy_test.py > > > from sympy import Symbol > > from math import * > > ^^^ Never ever use implicit imports (if possible). By writing this explicitly: > > from math import sqrt, exp > > it becomes clear, what is happening: > > > > > x = Symbol('x') > > i = 0 > > prior = 1 / sqrt(2*pi) * exp(-1*x**2 / 2) > > You are using math.exp() here, so it needs a floating point number, > but sympy doesn't know how to convert "x" to a floating point number, > thus you get the exception below. The solution is to replace the line > > from math import sqrt, exp > > with > > from sympy import sqrt, exp > > > > > > > p = 1 / (1 + exp(-1*discriminations[i]*(x - difficulties[1]))) > > q = 1 - p > > posterior = prior * q > > print posterior > > > But, when I ran this Python code, I got the following error message: > > Traceback (most recent call last): > > File "/Applications/eclipse/plugins/ > > org.python.pydev.debug_1.5.7.2010050621/pysrc/pydevd.py", line 978, in > > <module> > > debugger.run(setup['file'], None, None) > > File "/Applications/eclipse/plugins/ > > org.python.pydev.debug_1.5.7.2010050621/pysrc/pydevd.py", line 780, in > > run > > execfile(file, globals, locals) #execute the script > > File "/Users/yjlee/Documents/Worx/EclipseWorx/SymPyProjects/src/ > > sympy_test.py", line 44, in <module> > > prior = 1 / sqrt(2*pi) * exp(-1*x**2 / 2) > > File "/Library/Python/2.6/site-packages/sympy/core/basic.py", line > > 2103, in __float__ > > raise ValueError("Symbolic value, can't compute") > > ValueError: Symbolic value, can't compute > > > All I was trying to do was to get a product of two functions, and I > > could not figure out what I did wrong. > > > Could anyone tell me what I did wrong? > > Ondrej
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