Sampling with vectors at the same time

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

[Azzi Abdelmalek]

Can you explain what do you want to do?

[Azzi Abdelmalek]

What does that mean?

How can I make understand first vector is a sampling and second is a vector of values?

[Alfonso]

with sampling I mean repetition of the experiment with different d (scalar) values, that will be returned in this way:

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

for each experiment used for plotting out how evolves in this 20 exp the function "sample".

A vector is an array.

[Image Analyst]

d is not a scalar in your main program. d is an array. Perhaps you want to take a single value of d when you call sample, like sample(d(10)).

[Alfonso]

d is a scalar, i want to test my function with 20 different d values evolving from 1 to 20 so:

SUM (cos(2*pi*1*A) )
SUM (cos(2*pi*2*A) ) 
SUM (cos(2*pi*3*A) )
.....
so in the end i'll receive

Columns 1 through 11

     a     b     c     ..

Columns 12 through 20

    ...

scalar results of a sumatory of cosinus of de values in vector

PEXAMPLE: cos(33,3)+cos(45,3)+....(the sum as long as the lenght of the vector A). so should return an scalar.

d will be 1 -> cos(33,3)+cos(45,3)

then

d will be 2 -> cos(66,6)+cos(90,6)

then ...

[Image Analyst]

See the code in my comment.

[Alfonso]

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

    ...

Answer 1

[Dr. Seis]

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.

[Alfonso]

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]

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

Answer 2

[Image Analyst]

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.

[Alfonso]

Yes, it's sum(...). A is a vector of random values that will be added themelves, nothing to do with the number of experiments d i want to test out of the function. In reallity, but youre right, that's what i said.

I've changed SUM to sum and (2*pi*d.*A) and still the same problem.

Mybe i don't know how to plot, i want to plot the function with different d's how you would do it?

Thank you

[Image Analyst]

That can't be, unless you also redefine pi as an array. Did you run my code? Because it works fine. Is your A perhaps a 2 or 3 dimensional array, unlike the 1D array that you showed?

Also, your function sample() does not return any value, so what good does it do?

[Image Analyst]

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);

IMPORTANT NOTE: you're just sampling the cosine at multiples of 2*pi, so all the values will be 1 and all your sums will be 20.

[Alfonso]

No, d is allways a scalar i want to test 20 times first d will be 1 then d will be 2 then d will be 3, so the cos argument will groth x1 x2 x3 and i'll need to plot how the funtion evolves with different arguments.

[Image Analyst]

Okay....isn't that exactly what my code did? Did you see how I called the function 20 times with different scalar values of d, taken from the dMain array (the collection of all d's you want to use)?

[Alfonso]

Hi again, with your code in a new script file, it prompted:

    ??? Error: File: prueba.m Line: 8 Column: 1
    Function definitions are not permitted in this context.

    in the LINE: function theSum = sample(d)

I've created an script file with your code since the for is supposed to be inside a function. How do yo do to have 2 functions without calling a for at the main. This tool is expected to be used in my project so it would be cool that it was inside a function.

Thank you.

[Alfonso]

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]

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.

Answer 3

[Azzi Abdelmalek]

Maybe you mean indexing

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

[Alfonso]

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.

Answer 4

[Alfonso]

<< d=[1:1:20]

<< sample(d)

no more code needed.

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

    function sample(d)

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

    end

Answer 5

[Alfonso]

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]).