Need help with looping to populate matrix using if statement

clc;
clear all;
close all;

load('Stress_Strain.mat')

count = 0;

for i = 1:1000

      if Stress_Strain_2(:,2) == count;
      StressStrain(i,2) = Stress_Strain_2(i,2);
      end
      count = count + 0.001
  end

% for i = 1:1000
%     
% if Stress_Strain_2(i,2) = count && Stress_Strain_2(i,2) > 0.0999;
%    Percent_Strain_2(1,2) = Stress_Strain_2(i,2);
%    Percent_Strain_2(1,1) = Stress_Strain_2(i,1);
% elseif Stress_Strain_2(i,2) < 0.2001 && Stress_Strain_2(i,2) > 0.1999;
%    Percent_Strain_2(2,2) = Stress_Strain_2(i,2);
%    Percent_Strain_2(2,1) = Stress_Strain_2(i,1);

[KSSV]

What exactly you want to do? Explain the subject behind it not the coding thing.

Answer 1

[Walter Roberson]

http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F

Two floating point numbers constructed different ways often do not exactly equal each other. You should be testing for being "close" rather than being "equal".

If you have R2015a or later you should consider using imembertol()

You also have the problem that

if Stress_Strain_2(:,2) == count

means the same thing as

if all(Stress_Strain_2(:,2) == count)

which is to say that all of the items in the column would have to be the same value, all exactly equal to what is in "count". This is unlikely to be what you wanted. You did not describe your desired match condition, so I cannot repair the code. Possibly you want

if any(Stress_Strain_2(:,2) == count)

except with correction for tolerances. Perhaps

if ismembertol(count, Stress_Strain_2(:,1))

Answer 2

[Kevin Hout]

Thanks, Walter.

I was trying to take a value in the Stress column (at Strains equal to 0.001, 0.002, 0.003, etc) and populate it into a new table. I am trying to use an if statement, but it is not working.