Hi I am reposting this as I didn't get any answer the last time. I am working on discret wave equations and I need a symbolic expression for
$\frac{d^2 p(x,t)}{dt^2} - G_{\bar{x}\bar{x}}^T((1+2\epsilon) p(x,t)) - G_{\bar{z}\bar{z}}^T(\sqrt{(1+2\delta)} r(x,t)) =q$ where $G_{\bar{x}\bar{x}} & = cos(\theta)^2 \frac{d^2}{dx^2} + sin(\theta)^2 \frac{d^2}{dz^2} - sin(2\theta) \frac{d^2}{dx dz} \\ G_{\bar{z}\bar{z}} & = sin(\theta)^2 \frac{d^2}{dx^2} + cos(\theta)^2 \frac{d^2}{dz^2} +sin(2\theta) \frac{d^2}{dx dz} \\ $ however as_finite_diff doesn't allow any cross derivatives (d/dxdy) even so the documentation says it does (it only does if you define it and then only take d/dx or d/dy) The second problem is to take derivatives of product. It shouldn't be a problem as this is just another function but it doesn't work neither. thank you mathias louboutin -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sympy+unsubscr...@googlegroups.com. To post to this group, send email to sympy@googlegroups.com. Visit this group at https://groups.google.com/group/sympy. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/600c0b76-5c78-422f-98ab-a7d033a7c7e6%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.