You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: struct_orth.m
    path of file: ./repos/lrslibrary/libs/+tensorlab
    
    the code of the file until where you have to start completion: function [x,state] = struct_orth(z,task,size_mat)
%STRUCT_ORTH Rectangular matrix with orthonormal columns.
%   [x,state] = struct_orth(z,[],size_mat) computes x as a rectangular

    
function [x,state] = struct_orth(z,task,size_mat)
%STRUCT_ORTH Rectangular matrix with orthonormal columns.
%   [x,state] = struct_orth(z,[],size_mat) computes x as a rectangular
%   matrix of size size_mat with orthonormal columns, given the vector z.
%   The vector z should have length size_mat(2)*(size_mat(1)- ...
%   (size_mat(2)-1)/2). The structure state stores information which is
%   reused in computing the right and left Jacobian-vector products.
%
%   struct_orth(z,task,size_mat) computes the right or left Jacobian-vector
%   product of this transformation, depend