MutliVariable symbolic finite differences

[Mathias Louboutin]

Hi

I am working on PDE's and I am trying to get the symbolic expression for multivariabe finite differences

mainly I wan the expression for d/dx(d/dy f), however

d2pdxdy=as_finite_diff(p(x,y,z,t).diff(x,y),[x,x-h,y,y+h])

doesn't work, nor any possible combination. Is this just not implemented or am I doing it wrong.

cheers

mathias

[Aaron Meurer]

What is the answer that you would expect to get?

Aaron Meurer

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[Mathias Louboutin]

In this example case it would give 

.25 * ( p(x,y+h,z,t) - p(x,y,z,t) + p(x-h,y,z,t) - p(x-y,y+h,z,t) ) /h^2

But more generally I would want to be able to take the result of as_finite_diff as a new expression I can differentiate :

a = as_finite_diff ( f(.....).diff(x) )

b= as_finite_diff( a.diff(y) )

....... And so on

[Aaron Meurer]

As far as I can tell, the function only supports finite differences of
one variable at a time. My guess is that it wouldn't be too hard to
extend it to do what you want, though.

Aaron Meurer

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