Sampling with vectors at the same time

Question

Alfonso 2013-2-24

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采纳的回答： Dr. Seis

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Hello,

its a simple question, but i havent managed to solve it:

I have to sample a vector and the matlab doesn't understandme and prompts:

     ??? Error using ==> mtimes
     Inner matrix dimensions must agree.

I wanted to sample a SUM (cos(2*pi*d*A) )where A is a vector of many degrees value, so I have:

    function sample(d)
          A = [1,2,3,....]
          SUM (cos(2*pi*d*A) )
    end

and the input is:

d=[1:1:20]

How can I make understand first vector is a sampling and second is a vector of values? (The idea is plotting (sample,d) )

The fact is that the expresion of the vector is a real for each value of d so I should expect something returning results of the SUM of different d's like:

Columns 1 through 11
     1     2     3     4     5     6     7     8     9    10    11
Columns 12 through 20
    12    13    14    15    16    17    18    19    20

But it doesn't understand each

Thank you

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Image Analyst 2013-2-24

See the code in my comment.

Alfonso 2013-2-24

编辑：Alfonso 2013-2-24

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yes but A is NOT of twenty values, in my code A is 8128 and i just want 100 experiments anyway.. No more resolution needed, it has nothing to do because d is a scalar. in the end d will be a 1 or a 2 or a 3, it will be performed in 20 experiments or (100 in my code) (as 20 inputs are passed) and then returned this way:

Columns 1 through 11

a b c ..

Columns 12 through 20

...

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Answer 1

Dr. Seis 2013-2-25

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编辑：Dr. Seis 2013-2-25

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Try this:

d = 1:20;
A = [24,34,56,66,86];
plot(d,arrayfun(@(x)sum(cos(2*pi*A*x)),d))

Obviously, in this simple case, the answer will always be 5 for all d since we are dealing with integer multiples of 2*pi (and there are only 5 elements in A), but I think this is what you are looking for.

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Alfonso 2013-2-25

编辑：Alfonso 2013-2-25

That was PRO!! That's what i'm searching for, Thank you!!

I'll search with the arrayfunc to draw my function, one thousand thanks to all.

Azzi Abdelmalek 2013-2-25

To close the topic, you have to accept the answer which helped you

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Answer 2

Image Analyst 2013-2-24

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编辑：Image Analyst 2013-2-24

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What is SUM? Is it a custom function you wrote, or an array of yours, because it's not the built-in MATLAB sum() function because MATLAB is case sensitive.

Perhaps you meant something like this:

A = 1:20
d=[1:1:20]
cosA = cos(2*pi*d.*A)
theSum = sum(cosA)

Note the .* instead of * between d and A to do an element by element multiplication, not a matrix multiplication like you were trying to do.

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Alfonso 2013-2-25

编辑：Alfonso 2013-2-25

It worked typing 60% of your code on the command window but i need something more elegant, Matlab is quite stranger that i though.

Need help to write some code equivalent to this almost all in a function

Very grateful anyway.

Image Analyst 2013-2-26

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Alfonso, you need to read the getting started guide. You can't just type all that code into a single m-file because you can't have a script followed by a function in the same file. The main program can be in one m-file, and the other function in another m-file, OR if you want them to be in the same file, then you must have a function name at the beginning of the file with the same name as the m-file. For example if it's test.m, then your code would be

function test()
dMain = [1:1:20]
for k = 1 : length(dMain)
  % Call sample() once for each value of d
  theSumMain(k) = sample(dMain(k));
end
theSumMain % Print to command window
function theSum = sample(d)
  A = 1:20;
  cosA = cos(2*pi*d.*A);
  theSum = sum(cosA);

If it's like that they can all be in the same m-file. I guess I assumed that you knew this.

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Answer 3

Azzi Abdelmalek 2013-2-24

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编辑：Azzi Abdelmalek 2013-2-24

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Maybe you mean indexing

v=[2 3 5 4 10 20]
d=[2 3 1 4 5 6]
new_v=v(d)

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Alfonso 2013-2-24

I meant to perform multiple experiments due to an entry of different values the d only affects for each experiment the d is first 1, the sum is done, then the d is two, the sum is done, then the d is three....

and then the result is returned of the function with 20 different d's as 20 different inputs to the function, the matlab wants to understand is a vector to multiply and is only 20 experiments so D is an scalar.

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Answer 4

Alfonso 2013-2-24

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编辑：Alfonso 2013-2-24

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<< d=[1:1:20]

<< sample(d)

no more code needed.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

    function sample(d)
          A = [24,34,56,....]
          SUM (cos(2*pi*d*A) )
    end

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Answer 5

Alfonso 2013-2-24

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编辑：Alfonso 2013-2-24

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MAYBE Im complicating myself, forget about the 20 (Or 100)entries, how would you plot:

    function sample(d)
          A = [24,34,56,....]
          SUM (cos(2*pi*d*A) )
    end

I used to plot

plot (d,sample(d))

I want function to evolve non like an integer (0,1:0,1:20) instead, so i want increases of the X axis of 0,1 from 1 to 20 HOW WOULD YOU PLOT IT? I simplified in your example, but i don't want a deffault plotting progress, so i use multiple entry (d=[0,1:0,1:20]).