how to increase the run time of the matrix ?

Hey ,

I am runnng a code for finding the shorter path , i am able to do it easily for matrix of 37*37 but as I increase its value it start to take lot of time.I tried to preallocate few values in it but not able to do it easily.

I am attaching 2 files for the reference. less_time.m is of 37*37 matrix and more_time.m is of 148*148 matrix.

kindly guide me how to preallocate the values in it so that I can increase the time of the operations

[Jan]

If runtime matters, omit the brute clearing header "clc; clear all; close all". It is useless inside a function, but removes all loaded funtions from the memory. Reloading them from the slow disk is a waste of time.

[navanit dubey]

sure sir , I added them just to get the clean values in command window.

Thankyou for the response

Answer 1

[Matt J]

The best option might be to use Matlab's own shortestpath routine,

https://www.mathworks.com/help/matlab/ref/graph.shortestpath.html

[navanit dubey]

Thankyou for the answer sir, But I am working on something so thats why I wanted to increase the operation time.

[Matt J]

Don't you mean you want to decrease the operation time? Don't you want it to be faster?

[navanit dubey]

yes sir but I want that in my matlab file that I have attached to it as

Answer 2

[Jan]

Some standard ideas for improving the runtime:

• sqrt(X) is faster than X^0.5
• The JIT acceleration is more powerful, if you write one command per line. Avoid constructs like this: "mink=k;minl=m;minkl=PLkm;"
• Logical indexing is faster than numerical indexing.

     % Replace:     
     Nonzero=find(PLK); 
     PLKPLK=PLK(Nonzero);
     
     % by:
     PLKPLK = PLK(PLK ~= 0);

• This works, but the multiplication by 1 is confusing only, most of all in the combination with a lowercase L:

    D = zeros(l*1,l*1);
    % Nicer:
    D = zeros(l, l);  % But I avoid "l" consequently to reduce confusions    

• If you need 1 element only, do not waste time with searching all elements:

    Select=find(Pcum>=rand); 
    to_visit=LJD(Select(1));
    % Faster:
    Select = find(Pcum>=rand, 1); 
    to_visit=LJD(Select);    

• In line 110 I assume you want a vector, not a matrix: "PP=zeros(Len_LJD);" Use PP=zeros(Len_LJD, 1) instead.
• Then you can replace:

            PP=zeros(Len_LJD); 
            for i=1:Len_LJD 
               PP(i)=(Tau(W,LJD(i))^Alpha)*((Eta(LJD(i)))^Beta); 
            end 
            sumpp=sum(PP); 
            PP=PP/sumpp;%Build probability distribution
            Pcum(1)=PP(1); 
            for i=2:Len_LJD 
               Pcum(i)=Pcum(i-1)+PP(i); 
            end 
            Select=find(Pcum>=rand); 
            to_visit=LJD(Select(1));
    % By:
            PP       = Tau(W,LJD).^Alpha .* Eta(LJD).^Beta;
            PP       = PP / sum(PP);
            Pcum     = cumsum(PP);
            Select   = find(Pcum >= rand, 1); 
            to_visit = LJD(Select);

[navanit dubey]

Thank you so much sir for explaining each terms and for editing too. I have applied it to my matlab script.

[Jan]

Now use the profiler to find out, where the most time is spent. This is the place to optimize the code to gain more speed.