Sweeping initial conditions for a set of ODEs using parfor - matlab

Question

I am currently trying to use parfor to sweep across a range of initial conditions for a set of differential equations solved by ode45. The code works fine using two nested for loops but I was hoping parfor could make the process more efficient. Unfortunately, I have run into an issue where the solver is able to solve one of the combinations in the matrix representing initial conditions across a range of variables, but the others seem to have their initial values all set at 0, instead of the values specified by the initial conditions. It may have something to do with the fact that I need to create a matrix of zeros ('P') that the results will be written into, perhaps overwriting the initial conditions(?) Any help would be greatly appreciated.
Thanks,
Kyle
function help(C, R)
A = 0.01;
B = 0.00;
C = [0.001,0.01];
D = 0.00;
R = [1e-10,1e-9];
[CGrid,RGrid] = meshgrid(C,R);
parfor ij = 1 : numel(CGrid)
c2 = [A; B; CGrid(ij); D; RGrid(ij)];
[t,c] = ode45('ode_sys',[0:1:300],c2);
for k=1:length([0:1:300])
for l=1:length(c2)
if c(k,l)<0
c(k,l)=0;
end
end
end
P = zeros(301,5,numel(R),numel(C));
temp = zeros(301,5);
temp(:,1) = c(:,1);
temp(:,2) = c(:,2);
temp(:,3) = c(:,3);
temp(:,4) = c(:,4);
temp(:,5) = c(:,5);
P(:,:,ij)=temp;
parsave('data.mat', P);
end
end

Answer 1

You have one error, and a few opportunities to simplify the code.
In the parfor loop, you have this line P = zeros(301,5,numel(R),numel(C)); which overwrites P with all zeros at each iteration. Put this before the parfor loop.
The first double-for loop that makes negative elements of c zero can be done using max(c,0), which should be more efficient. You can also do P(:,:,ij)=c(:,1:5) directly.
So you can replace your parfor loop with
P = zeros(301,5,numel(R),numel(C));
for ij = 1 : numel(CGrid)
c2 = [A; B; CGrid(ij); D; RGrid(ij)];
[t,c] = ode45('ode_sys',0:300,c2);
c = max(c,0);
P(:,:,ij) = c(:,1:5);
parsave('data.mat',P);
end