# how can I vectorize my code when multiple variables are present

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Deepa Maheshvare on 21 Feb 2021
Edited: Deepa Maheshvare on 23 Feb 2021
Hi All,
This is a follow up to my previous question here.
I'm trying to figure out how to vectorize my code when multiple variables are present. The following is the toy model with odes for 2 variables (Please note the code may not make much sense, in my real system variables w and u are coupled. Also, in the actual system the number of variables in the model is uder-defined. For this reason, I am looping through the variables in the for-loop).
global mat1 mat2 k nvar var npts
k = 2;
nvar =2;
var = ["w", "x"];
npts=10;
mat1=[
1 -2 1 0 0 0 0 0 0 0;
0 1 -2 1 0 0 0 0 0 0;
0 0 1 -2 1 0 0 0 0 0;
0 0 0 1 -2 1 0 0 0 0;
0 0 0 0 1 -2 1 0 0 0;
0 0 0 0 0 1 -2 1 0 0;
0 0 0 0 0 0 1 -2 1 0;
0 0 0 0 0 0 0 1 -2 1;
];
mat2 = [
1 -1 0 0 0 0 0 0 0 0;
0 1 -1 0 0 0 0 0 0 0;
0 0 1 -1 0 0 0 0 0 0;
0 0 0 1 -1 0 0 0 0 0;
0 0 0 0 1 -1 0 0 0 0;
0 0 0 0 0 1 -1 0 0 0;
0 0 0 0 0 0 1 -1 0 0;
0 0 0 0 0 0 0 1 -1 0;
];
w0 = [2 0 0 0 0 0 0 0 0 0]';
x0 = [1 0 0 0 0 0 0 0 0 0]';
z0 = [w0; x0];
tspan = 0:0.01:0.5;
f0 = fun(0, z0);
joptions = struct('diffvar', 2, 'vectvars', 2, 'thresh', 1e-8, 'fac', []);
J = odenumjac(@fun,{0 z0}, f0, joptions);
sparsity_pattern = sparse(J~=0.);
options = odeset('Stats', 'on', 'Vectorized', 'on'); %, 'JPattern', sparsity_pattern);
ttic = tic();
[t, sol] = ode15s(@(t,z) fun(t,z), tspan , z0, options);
ttoc = toc(ttic)
fprintf('runtime %f seconds ...\n', ttoc)
plot(t, sol)
function Zstruct = get_Zstruct(z)
global nvar var npts
temp = reshape(z, npts, []);
for i = 1:nvar
Zstruct.(var(i)) = temp(:,i);
end
end
function dz = fun(t,z)
global nvar var mat1 mat2
fprintf('size of z %d %d...\n', size(z))
dz = zeros(size(z), 'like', z);
Zstruct = get_Zstruct(z);
F =[];
for i = 1:nvar
x = Zstruct.(var(i));
f = zeros(size(x), 'like', x);
f(1,:) = 0;
f(2:9,:) = mat1*x + mat2*x;
f(10,:) = 2*(x(end-1) - x(end));
end
F(:,:) = vertcat(F,f);
end
I tried to check the size of z and it inconsistent for different function calls.
size of z 20 1...
size of z 20 20...
size of z 20 1...
size of z 20 1...
:
size of z 20 1...
size of z 20 1...
size of z 20 1...
size of z 20 20...
I'm sure the mistake is in the function Zstruct = get_Zstruct(z). I'm not sure how to vectorize here. Could someone please help me with this?
Deepa Maheshvare on 23 Feb 2021
@Walter Roberson I'm sorry, I didn't understand your comment completely .
temp is a double, sorry, I'm a bit confused how to use cell2struct() here. Also, I couldn't understand why the size of `z` varies from 20 x 1 to 20 x 20.

darova on 22 Feb 2021
Try to remove parenthesis
Deepa Maheshvare on 23 Feb 2021
when I try removing the paranthesis
Unable to perform assignment because the indices on the left side are not compatible with the size of the right side.
Error in cse_2_21_21>get_Zstruct (line 50)
Zstruct.var(i) = temp(:,i);
Error in cse_2_21_21>fun (line 58)
Zstruct = get_Zstruct(z);
Error in cse_2_21_21 (line 34)
f0 = fun(0, z0);

R2019b

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