MATLAB: Simple counter won’t trigger if statement

if ignored

Hello, there is something strange happening when I run this code (workspace is empty before I run this)
 tplot = 0;
 for t = 1:100
    tplot = tplot+0.1;
    if tplot == 1
        tplot
        tplot = 0;
    end
 end
It never jumps inside the if block. When I increase tplot by 0.2 or 0.5 instead of 0.1 it works. I used the debugger to see what's happening when I use 0.1. When tplot reaches 1.0000 it totally ignores the if part.
Do you encounter the same problem? If so, what could be the reasen for this?

Best Answer

This is a classic beginner's problem. Your computer uses binary floating point numbers, and as such cannot exactly represent the fraction 0.1. For that reason after you have multiplied the approximation to 0.1 by ten, the result won't be an exact 1. It will probably be off in the least bit or bits. You should allow room for a small deviation from an exact 1 in your 'if' statement.
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