how to transfer an allocated array on GPU to solver-apply

[ztdepztdep]

The d_b and d_x is two double arraies which have been allocated on GPU. I want to know how to transfer it to the solver-apply.
I tried to use the following code:
solver->apply(gko::lend(d_b), gko::lend(d_x));
but it doesn't wok.

[pratikvn]

Can you please let us know the following info:

• Are d_b and d_x of type gko::matrix::Dense<double> ?
• Can you elaborate on what errors you are getting ? Maybe add the error here below ?

[yhmtsai]

I copy my reply from the same discussion #1131

Are the type of d_b and d_x double*?
If they are, the solver needs to use the gko::matrix::Dense<double>* type.
You can create the Dense matrix by reading a mtx file.
ex. gko::read<gko::matrix::Dense<>>(std::ifstream("filepath"), exec);
or create the Dense first then fill in the data

auto x = gko::matrix::Dense<>::create(exec, gko::dim<2>(n, 1));
// copy the data to x->get_values()

or create the Dense on the preallocated array
auto x = gko::matrix::Dense<>::create(exec, gko::dim<2>(n, 1), gko::array<double>::view(exec, n, d_x));
note. array view to indicate the size and location for the plain pointer.

[ztdepztdep]

how to copy the value to x->get_values(), need i to use clone?
the second command auto x = gko::matrix::Dense<>::create(exec, gko::dim<2>(n, 1), gko::array::view(exec, n, d_x));
give many errors
/home/ztdep/lib/ginkgo/include/ginkgo/core/base/polymorphic_object.hpp(737): error: no instance of constructor "gko::matrix::Dense::Dense [with ValueType=double]" matches the argument list

[yhmtsai]

Sorry, I miss a parameter stride in the end.
you can use dest_exec->copy_from(src_exec, num_elems, src_ptr, dest_ptr) to copy the value