If we have this expression tra{m}.X, what sould "tra" be ?

I am trying to understand a function that trains a simple multiple Kernel SVM on training data with given parameters (smksvm(tra,par)), and along the code "tra" is used in a way that I didn't know how to apply it on my data (which is a feature matrix of 77 patients), I know it should be defined as a cell from the expression but all my attempts have failed drastically, any suggestions ?

[Stephen23]

tra appears to be a cell array containing a (scalar) structure. Better would be to change the code to use a non-scalar structure:

https://www.mathworks.com/help/matlab/matlab_prog/access-multiple-elements-of-a-nonscalar-struct-array.html