Using diff() in a for loop
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I'm trying to plot the difference between two values against an integer, but I get the error "Difference order N must be a positive integer scalar" when using diff. I currently have a function to estimate the volume of a sphere, and another to compare it to the real volume and plot it. Below is my code:
.m
function volume = approximate(b)
for k = 0:b
sum = ((-1).^k) / (2 * k + 1);
end
radius = 46.8;
volume = 4/3 * (4 * sum) * radius.^3;
end
difference.m
b = 0:1:10;
radius = 46.8;
trueValue = (4/3) * pi * radius.^3;
for i = 1:length(b)
difference = diff(approximate(i), trueValue);
end
plot(b, difference);
采纳的回答
Did you read the documentation of diff already?
doc diff
It calculates the difference between neighboring elements of a vector and the 2nd input is the difference order.
The code contains more problems:
- Do not use "sum" as a name of a variable. This shadows the builtin function with the same name and this causes unexpected behavior frequently.
- approxvol is undefined. What about replying a vector from your function approximate?
- I assume you want simply: difference = approxvol(i) - trueValue, but this overwrites difference in each iteration. Either use difference(i) = approxvol(i) - trueValue or better omit the loop:
difference = approxvol - trueValue;
Matlab can work with vectors directly.
2 个评论
Brittany Toohey
2017-4-9
Jan
2017-4-9
Note that both loops in your code a meaningless, because they overwrite the output in each iteration.
function volume = approximate(b)
for k = 0:b
sum = ((-1).^k) / (2 * k + 1);
end
Perhaps you mean:
function volume = approximate(b)
S = 0;
for k = 0:b
S = S + ((-1).^k) / (2 * k + 1);
end
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