indexing with global variables in function statements

Hi! can I not include a global variable in an output in a function like this:

function sigma_v_eff_sona(zone_number,1)=effective_stresses()

when I declare zone_number as global variable in effective_stresses. Do I have to skip the index zone_number in the output statement since I have declared zone_number as a global variable in the mentioned function?

[KL]

The question is why do you need it as a global variable?

[Muazma Ali]

because i am using it in many functions

Answer 1

[Walter Roberson]

The left hand side of the = of a function statement must be plain variables names, not indexed, not structure references, not cell array references.

In MATLAB, if you want to have a function that changes only some portions of the output variable, then the variable must be input as well, such as

function sigma_v_eff_sona = effective_stresses(sigma_v_eff_sona) 
  global zone_number
  sigma_v_eff_sona(zone_number,1) = ...

[Muazma Ali]

so if i have a while loop in the beginning and want to add the elements in the array called sigma_v_eff_sona afterwards as the while loop proceeds using the mentioned function, so i have to have it both as input and output?

[Walter Roberson]

If you are adding new content to the end of sigma_v_eff_sona then you can do

while ....
   ...
   sigma_v_eff_sona(end+1) = effective_stresses(...);
   ...
end

However it is more efficient to pre-allocate arrays when practical.

sigma_v_eff_sona = zeros(1,100);
svefs_count = 0;
while ...
  ...
  svefs_count = svefs_count + 1;
  sigma_v_eff_sona(svefs_count) = effective_stresses(...);
  ...
end

[Muazma Ali]

ok, this is how it looks like in my script:

zone_number=0;
while .....
zone_number=zone_number+1;
max_pressure=maks_trykk_perm() % this function calls sigma_v_effective_stress=effective_stresses()

in this case where should I preallocate the array called sigma_v_effective_stress?

in my programme i have several such arrays somehow within the while loop but not directly. They are supposed to have max 40 values each.

[Walter Roberson]

I think you should rewrite as a for loop. Perhaps something similar to

max_zones = 40;
max_pressure = zeros(1, max_zones);
old_max_pressure = inf;

for zone_number = 1 : max_zones
  this_pressure = maks_trykk_perm();
  if abs( this_pressure - old_max_pressure) < 0.001
    break;   %close enough to end the loop early?
  end
  max_pressure(zone_number) = this_pressure;
  ...
end

Answer 2

[the cyclist]

Are you getting the error "Unexpected MATLAB expression"? The global variable is irrelevant. The following is not a valid way to output from a MATLAB function.

function x(1) = answerTest()
  x = [3 2];
end

You need to do the indexing in the function, then output a "whole" variable.