Hi @Aep93,
a total-degree basis in 44 dimensions with degree 5 has already more than a million elements: {44+5 \choose 5} = 1906884
Creating an even larger basis might cause Matlab to run out of memory, and it does not make sense, because if you have a huge number of regressors in the basis, you also need a huge number of points in the experimental design. How many experimental design points do you have available?
If you have a high-dimensional problem, common ways to reduce the size of the basis are using q-norm (hyperbolic) truncation or restricting the maximum interaction order to 2 or 3, see e.g. Question regarding PCE and LOO error. And in case you don’t use it yet, you should try UQLab’s degree and q-norm adaptivity, such as
MetaOpts.Degree = 1:5;
You could also try to first identify the important variables in your model, and then build a meta-model only on these.
I hope this helps, let us know how you made it work! 