How to improve the performance of nested for loop

Question

1.00/5 (1 vote)

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The code runs true. However the nested for loop runs 3.5 second and I have to run this method 50 times. So it takes too much time. How can I optimize?

C#

object.Y is jagged array [1406][21]
object.dif is jagged array [1406][1405]
object.E = 21

After Y jagged array filled up with double and NAN, I sort every row then I find index of non NAN elements.

What I have tried:

C#

private void Calculate(Obj object)
{
  double sum = 0;
  int i = 1406;
  int j = 1405;
  for (int t = 0; t < i; t++)
  {
    object.dif[t] = new double[j];
    for (int l = 0; l < j; l++)
    {
      if (Math.Abs(t - l) > object.E)
      {
        for (int k = 0; k < object.E; k++)
        {
          sum += (object.Y[t][k] - object.Y[l][k]) * (object.Y[t][k] - object.Y[l][k]);
        }
        object.dif[t][l] = Math.Sqrt(sum);
      }
      else
        object.dif[t][l] = double.NaN;
    sum= 0;
    }
  }
}

//With Parallel For but because of Sum, everytime Y matrix give different results
private void Calculate(Obj object)
{
  double sum = 0;
  int i = 1406;
  int j = 1405;
   Parallel.For(0,i,t=>{
    object.dif[t] = new double[j];
    for (int l = 0; l < j; l++)
    {
      if (Math.Abs(t - l) > object.E)
      {
        for (int k = 0; k < object.E; k++)
        {
          sum += (object.Y[t][k] - object.Y[l][k]) * (object.Y[t][k] - object.Y[l][k]);
        }
        object.dif[t][l] = Math.Sqrt(sum);
      }
      else
        object.dif[t][l] = double.NaN;
    sum= 0;
    }
  });
}

Posted 12-Jul-17 7:31am

mdaemon

Updated 13-Jul-17 0:29am

v4

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Patrice T · Answer 1 · 2017-07-12T13:32:00

This code is pretty much minimum and nothing can be removed without knowing its use.
To reduce runtime, the only possibility is using parallel processing.

Quote:
It cant because of sum.

If you do careful analyze of your code, you will see that sum is not a problem.

Quote:
I added the new method that I tried with parallel.for

And it don't work.
You need to analyze what the code do !
In which part of the code do you need sum ?
Where do you calculate sum ? Where do you use sum ?
Where do you initialize sum ?
What happen to sum when you parallelize the loop ?
Use the debugger to see what your code is doing.
-----
There is a tool that allow you to see what your code is doing, its name is debugger. It is also a great learning tool because it show you reality and you can see which expectation match reality.
When you don't understand what your code is doing or why it does what it does, the answer is debugger.
Use the debugger to see what your code is doing. Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute.

Debugger - Wikipedia, the free encyclopedia[^]
Visual Basic / Visual Studio Video Tutorial - Basic Debugging - YouTube[^]
Visual Basic .NET programming for Beginners - Breakpoints and Debugging Tools[^]

Debugging C# Code in Visual Studio - YouTube[^]

The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't find bugs, it just help you to. When the code don't do what is expected, you are close to a bug.

RickZeeland · Answer 2 · 2017-07-12T08:17:00

Solution 1

If you have a powerful processor with enough cores, you could use parallel processing, see: Task Parallel Library: 1 of n[^]

Posted 12-Jul-17 8:17am

RickZeeland

Comments

mdaemon 12-Jul-17 16:12pm

It cant because of sum. I try to use parallel.for but everytime Y array is produced differently.