reshape makes a view, and views are cheap. Don't worry about this. BTW, I would love to add a collocation method to JuliaDiffEq. Would you consider making this a package?
On Sunday, October 30, 2016 at 3:52:37 AM UTC-7, Alexey Cherkaev wrote: > > I'm writing RadauIIA (for now, fixed order 5 with 3 points) method for ODE > BVP (basically, collocation method). In the process, I construct an overall > non-linear equation that needs to be solved. It takes "mega-vector" x[j] as > an argument. However, internally it is more convenient to reshape it to > y[m,i,n] where m is the index of original ODE vector, i is the index of the > collocation point on time element (or layer) and n is time element index. > Also, some inputs to the method (ODE RHS function and BVP function) expect > z[m]-kind vector. So far I chose to pass a @view of the "mega-vector" to > them. > > The alternatives for reshaping and @view would be: > > - Use the inline function or a macro that maps the indices between > mega-vector and arrays (I've tried it, didn't see any difference in > performance or memory allocation, but @code_warntype has less "red" spots) > - Copy relevant pieces of mega-vector into preallocated arrays of > desired shape. This can also be an alternative for @view. > > Is there some kind of rule of thumb where which one would be preferable? > And are there any high costs associated with @view and reshape? > >
