MATLAB: Is MATLAB running slow? 2013a vs 2011a

2011a2013arunning slowslow solving time

Hi everyone,
I am running an m-file in Matlab 2013a, which takes roughly 20sec to complete. However, when a friend runs the same code in 2011a it takes a fraction of a second to complete. What could be causing this in my 2013a installation?
Our PCs have the same components so that is not the culprit.
Just a note; the code I am testing is very simple, for the most part just for loops.
Thanks
 clc; clear all; close all;
 format compact
 % Define number of cells in x and y
nx = 20; 
ny = 20;
uw = 1;
 % Define cell length in x and y
dx = 1.0/nx; 
dy = 1.0/ny;
 % Relaxation Parametres
relax1 = 0.2; 
relax2 = 1.2;
relax3 = 0.2;
 % Reynolds Number
re = 100; 
 nu = 1/re;
 kappa = 1/re;
 rex = 2.0/dx/dx + 2.0/dy/dy;
 % Initialise the streamfunction and vorticity everywhere.
for i = 1:nx+1 
    for j = 1:ny+1
        psi(i,j) = 0.0; % Streamfunction
        w(i,j) = 0.0;
        x(i,j) = (i-1)*dx;
        y(i,j) = (j-1)*dy;
        T(i,j) = 0.0;
        if j == ny+1
            T(i,j) = 1.0;
        end
    end;
 end;
 for k = 1:20000 %main loop - iterate until convergence.
    adu = 0.0;
    adv = 0.0;
    psimin = 1000000.0;
    psimax = -1000000.0;
    for i = 2:nx %sweep through all internal points on the grid
        for j = 2:ny %updating until convergence.
        wimj0 = w(i-1,j); %for the vorticity equations these values
        wipj0 = w(i+1,j); %may have to be modified at the points
        wi0jm = w(i,j-1); %adjacent to the walls
        wi0jp = w(i,j+1);
            % Boundary Adjacent Conditions
            if(i == 2) 
                wimj0 = -2.0*psi(i,j)/dx/dx;
            end;
            if(i == nx)
                wipj0 = -2.0*psi(i,j)/dx/dx;
            end;
            if(j == 2)
                wi0jm = -2.0*psi(i,j)/dy/dy;
            end;
            if(j == ny)
                wi0jp = -2.0*(psi(i,j)+dy*uw)/dy/dy;
            end;
            %this is the update for w(i,j) from the FDE.
            wij = (nu*((wipj0+wimj0)/dx/dx + (wi0jp+wi0jm)/dy/dy)...
                + (((psi(i+1,j)-psi(i-1,j))*(wi0jp-wi0jm)-((psi(i,j+1)...
                -psi(i,j-1))*(wipj0-wimj0)))/(4*dx*dy)))/(nu*rex);
            dw = wij - w(i,j);
            %compute the difference between new and old value.
            w(i,j) = w(i,j) + relax1*dw;
            %update using relaxation
            %update equation for the streamfunction
            psiij = ((psi(i+1,j)+psi(i-1,j))/dx/dx + ...
                (psi(i,j+1)+psi(i,j-1))/dy/dy + w(i,j))/rex;
            dpsi = psiij - psi(i,j);
            psi(i,j) = psi(i,j) + relax2*dpsi;
            if(psi(i,j)>psimax) %determine maximum and minimum streamfunction
                psimax = psi(i,j);
            end;
            if(psi(i,j)<psimin)
                psimin = psi(i,j);
            end;
        ddu = abs(dpsi); %compute maximum change in solution over full sweep.
        ddv = abs(dw);
            if(ddu>adu)
            adu = ddu;
            end;
            if(ddv>adv)
            adv = ddv;
            end;
        end;
    end;
 % k
 % psimax
 % psimin
 % adu
 % adv
    % Exit loop if converged
    if(adu<1.0e-4 && adv<1.0e-4) 
        break;
    end;
 end;
 % Compute the temperature distribution
for l = 1:10000
    adT = 0.0;
    for i = 1:nx+1
        for j = 1:ny+1
            if j ~= 1 && j ~= ny+1
                if i == 1 % Using a forward difference scheme on the psi differential
                    Tij = (kappa*((T(i,j+1)+T(i,j-1))/dy/dy) + ...
                        (psi(i+1,j)-psi(i,j))*(T(i,j+1)-T(i,j-1))/(2*dx*dy))/(kappa*2/dy/dy);
                elseif i == nx+1 % Using a backward difference scheme on the psi differential
                    Tij = (kappa*((T(i,j+1)+T(i,j-1))/dy/dy) + ...
                        (psi(i,j)-psi(i-1,j))*(T(i,j+1)-T(i,j-1))/(2*dx*dy))/(kappa*2/dy/dy);
                else
                    Tij = (kappa*((T(i+1,j)+T(i-1,j))/dx/dx + ...
                        (T(i,j+1)+T(i,j-1))/dy/dy) + ...
                        (psi(i+1,j)-psi(i-1,j))*(T(i,j+1)-T(i,j-1))/(4*dx*dy)...
                        - (psi(i,j+1)-psi(i,j-1))*(T(i+1,j)-T(i-1,j))/(4*dx*dy))/(kappa*rex);
                end;
                dT = Tij - T(i,j);
                T(i,j) = T(i,j) + dT*relax3;
                ddT = abs(dT);
                if(ddT>adT)
                    adT = ddT;
                end;
            end;
        end;
    end;
    if adT < 1e-6
        break
    end
 % l    
 % adT   
 end;
 k
 psimin
 adu
 adv
 l
 adT
 % Plot solution.
 for i = 1:10
 v(i) = -(i-1)*0.01;
 end;
 for i = 11:20
 v(i) = (i-10)*psimax/10;
 end;
 figure(1)
 contourf(x,y,psi,v);
 xlabel('x')
 ylabel('y')
 title('Streamfunction')
 colorbar
 figure(2)
 contourf(x,y,T)
 xlabel('x')
 ylabel('y')
 title('Temperature Distribution (\circC)')
 colorbar

Best Answer

I tried your code on my machine in both R2011a and R2014a, and as posted it is indeed quite a bit slower in R2014a. You can get nearly all the speed back if you make your code a function rather than a script. See this page for more about functions if you're not already used to writing them.
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