Matlab creates a local copy every time I use/modify a global variable

Dear all,

I've noticed that Matlab spends a lot of time executing quite simple code with about linear complexity. I've generated a C code of this function using Embedded Matlab Compiler as follows:

rtwcfg = emlcoder.RTWConfig;
rtwcfg.CustomSource = 'main.c';
% Warning: Matlab uses a lot of (6Gb) memory to  generate C code.
emlc -T rtw:exe -s rtwcfg  -global {'tree', tree, 'tree_size', tree_size,'test_cycle', test_cycle, 'max_nodes', max_nodes} test7_SOC_SARSA_BSP1_UDDS_cycle_T_embedded;

The executable runs even worse the original Matlab programm. In the C code I see that every time the global variable "tree" is used Matlab copies it into another local variable. For example:

if (rand() > epsilon) 
      [~, a] = max(tree(s).Q);
else
  %a = randi(nactions, 1);
end

is transformed to:

eml_a = 0.0;
eml_r = m_refp1_genrandu(twister_state);
if(eml_r >= 0.0) {
  m_cast(tree, eml_hoistedExpr);
  m_b_max(eml_hoistedExpr[(int32_T)eml_s - 1].Q, &eml_r, &eml_a);
} else {
  /* a = randi(nactions, 1); */
}

Here is the code of the m_cast() function:

void m_cast(const struct sDbrZRlzGvadVfPbni0fyYH eml_x[50001], struct
sDbrZRlzGvadVfPbni0fyYH eml_y[50001])
{
int32_T eml_j;
for(eml_j = 0; eml_j < 50001; eml_j++) {
  eml_y[eml_j] = eml_x[eml_j];
}
}

as you may observe it copies first input arg to the second one.

Why does Matlab create these copies? Is it possible to avoid them? Thank you very much in advance for any help and your time,

Regards, Dmitry

Answer 1

[Kevin]

The cast might be caused by a mismatch in the number of dimensions in the indexing expression tree(s). What is size(tree)? If it is [1 50001] then you may be able to eliminate the cast by writing tree(1,s) rather than tree(s).