Error-check spacing of a vector

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Zheng Sen Ter on 29 Sep 2021
Commented: Zheng Sen Ter on 29 Sep 2021
Hi, I encountered a problem doing integration using simpson 3/8 or 1/3 or trapezoid rule on 2 sets of vectors x and y. It turns out that the error occur in my function file. For integration, i need to check the spacing of vector x to be the same first.
let me put it like this example:
range = [10,20];
p = 1e-3;
x = range(1):p:range(2);
% check spacing
n = length(x)
h = x(2)-x(1)
for i = 2:n-1
if x(i+1) - x(i) ~= h
error('x spacing not correct')
end
end
Although each spacing of x should be the same, which is p=1e-3. However, the for loop gives error. (error: x spacing ot correct) . It doesnt give error if p = 1.
Is this because of the limitation of Matlab? Sorry if this is a pretty basic theory i should know.

Geoff Hayes on 29 Sep 2021
Zheng - you are trying to compare two floating point numbers using (in this case) the inequality operand. When comparing two floats or doubles, you need to use a tolerance as described at Compare floating-point numbers as the equality (or inequality) operands will not necessarily give the desired result.
Zheng Sen Ter on 29 Sep 2021
Got it. Thanks!

R2021a

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