use vector as input

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Vincent Degonda
Vincent Degonda 2021-2-28
回答： Steven Lord 2021-2-28
I want to give each input of a vector as an argument to my function to recive a list of values that i can then plot (my goal is to plot the time it takes to execute the function for a given n). The problem is, that i only get the output of the first entry of the vector. What did I do wrong?
>> n = [1:1:10];
>> [a,b] = calcEulerSum2 (n)
it returns only calcEulerSum2(1)
function [e, a] = calcEulerSum2(n)
den = 1;
e = 1;
tic
for i = 1 : n
den = den * i;
e = e + 1/den;
end
a = toc;
end
  2 个评论
dpb
dpb 2021-2-28
"What did I do wrong?"
We dunno and have no way to know -- you forgot to show us the code for calcEulerSum2
dpb
dpb 2021-2-28
What do you expect for output and what is the expected input?
I think you aren't using for as documented/wanted here.
Try at the command line to see what you get for:
n=1:3;
for i=1:n, disp(i), end
followed by
for i=n, disp(i), end
and see if that doesn't clear up the mystery.

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回答（2 个）

Robert U
Robert U 2021-2-28
Hi Vincent Degonda,
Your for-loop call is not providing what you expected. Your input variable is a vector already. dpb tried to lead you to that. Output in vector form would need an indexing of your output variable.
function [e, a] = calcEulerSum2(n)
den = 1;
e = 1;
tic
for i = n
den = den * i;
e(end+1) = e(end) + 1/den;
end
a = toc;
end
Kind regards,
Robert
Steven Lord
Steven Lord 2021-2-28
So you want to compute the value of e and the time required to compute that value for each element of n? A couple of suggestions:
function [e, a] = calcEulerSum2(n)
den = 1;
e = 1;
Make the variable e an array of ones the same size as n. The documentation page for ones include a couple of examples that you can use as a model.
tic
Before you start timing, you'll need a loop over the elements of the input. Use the numel function that gives the number of elements in an array for this loop.
for whichElement = <you fill this in> % I added this to your code
Continuing on with the code you already wrote:
for i = 1 : n
You don't want to use the whole n array here, just one element. Which element should you use instead of n here? I think you can guess.
den = den * i;
e = e + 1/den;
Since e is now an array here, not just one value, you need to operate on and assign back into a particular element. Which element of e? It should be clear.
By the way, you'll need to adjust how (or more precisely where/when) you initialize den. If the first element of n was 3, what should den be when you start processing the second element of n and what will it actually be?
end
a = toc;
end
Since I added a for loop to your code, you'll need one more end statement. Where should the for loop I added end?

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