evaluating a string as an expression

[Adam Ferestad]

I am looking for a way to type a math expression into a string parameter, then evaluate it in the function.  Specifically I am working on writing a Monte Carlo numerical integrator for a project I am doing that needs some integrals, but I am wanting to be able to use it for any expression.  I want to be able to pass it the expression and bounds to evaluate, but I am unsure of how to actually make it evaluate the string as anything but.  The old chrsraw() expression function did what I needed it to on an old project, but I am aiming to do this purely with VEX.

 

This will eventually turn into a random variable node with more control over the distributions, but I need the gamma function for several of them, which requires an integral calculation, as do several others.

 

As a side note, I got the Monte Carlo working for the gamma function, but it just couldn't get an accurate number in a good enough time, but I was able to get a rectangular rule that gets close enough.  

Edited October 4, 2014 by Adam Ferestad

[edward]

Evaluate it in what function where?

[Adam Ferestad]

Something like this:
 

sop

something(string expression, {variables})

{

addattribute("result",evaluate(expression))

}

 

obviously this is grossly oversimplified, but I want to have a parameter on my UI in the parameters pane that accepts me typing in something like pow(x,x)-3*x-2 and then actually processes it in the code.  

 

the end goal for this thread is that I can pass a math expression to a function call and have the function execute the expression with given variables.

Edited October 5, 2014 by Adam Ferestad

[edward]

Isn't that the same thing as what the new wrangler nodes do with the Snippet VOP?

[Adam Ferestad]

I am unfamiliar with those nodes.  Could you point me in the direction of the documentation for them to see if I can apply them.  I am really trying to do it in VEX, but if I have to do it using VOPs I suppose I can.

[Guest tar]

Hey Adam - the Wrangle nodes are Vex - The online docs have it all. e.g. 

 

http://www.sidefx.com/docs/houdini13.0/nodes/sop/pointwrangle

[mitul]

if you are using python

eg. you want to set expression in tx of point node

 

my_node = hou.node('/obj/geo1/point1')

my_tx = my_node.parm('tx')

my_tx.deleteAllKeyframes() # to delete any existing expression

my_tx.setExpression ('$TX + rand($PT)')

Edited October 27, 2014 by mitul