Unexpected result linspace function

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Nguyen Trung Kien
Nguyen Trung Kien 2018-11-30
评论： Nguyen Trung Kien 2018-11-30
Today I am working with
linspace
function. I used it as
x = linspace(x1,x2,(x2-x1)/deltax+1)
When I passed the value of x1, x2, deltax as:
x1=0.2;
x2=0.5;
deltax=0.1;
I got the result
x = 0.2 0.35 0.5
I try again with
x = linspace(0.2, 0.5, 4)
the result was as expected:
x = 0.2 0.3 0.4 0.5
I do not know it is a bug or other side effect of linspace function. Please help me to understand this. Because if I try:
x1=0.2;
x2=0.6;
deltax=0.1;
The result was good
x = 0.2 0.3 0.4 0.5 0.6
Thank you in advance for your consideration. The following image is the console command I tried:
Capture.PNG

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采纳的回答

Mark Sherstan
Mark Sherstan 2018-11-30
It is due to round off error. Linspace documentation states the following regarding the fuction: If n is not an integer, linspace rounds down and returns floor(n) points. The number is really close to 4 but not 4 so linspace is rounding the number down to 3 or "flooring" it. The other case is exactly 5 and you dont have that issue. Try the following in MATLAB and you will see:
x1=0.2;
x2=0.5;
deltax=0.1;
x = (x2-x1)/deltax+1
x == 4
>> False
x1=0.2;
x2=0.6;
deltax=0.1;
x = (x2-x1)/deltax+1
x == 5
>> True
  1 个评论
Nguyen Trung Kien
Nguyen Trung Kien 2018-11-30
Thank you so much for your explaination. This helped me to understand and not confuse more.

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