1

i want to create a single dimensional array in MATLAB inside for loop, please help with below code:

count = 0;  
for i=1:10  
arr = count;  
count = count+1;    
end

when i execute this small code i got 9 as result for arr.

Instead of this i want to have an array arr with 10 values of count for each iteration of i, please help.....

4

3 に答える 3

8

There are several ways to create arrays in Matlab. The ones you will encounter most often are

  • via a range expression:

    a = 1 : 10;    % Creates a row vector [1, 2, ... 10]
a = (1 : 10)'; % Creates a column vector [1, 2, ... 10]^T.

  • via generating functions:

    a = zeros(1, 10); % Creates a 1x10 (=row vector) containing 10 zeros.
a = zeros(10, 1); % Creates a 10x1 (=column vector) containing 10 zeros.

    Other generating functions are ones to create vectors/matrices whose elements are all 1, rand to generate vectors/matrices with uniformly distributed random numbers, randn for random matrices with Gaussian distribution and so on.

  • via concatenation (this is slow, but easy to implement and sometimes not avoidable):

    % Create a vector containing the numbers 1, 4, 9, 16, ... 100.
a = [];
for idx = 1 : 10
    a = [a, idx^2];   % Creates a row vector.
    % a = [a; idx^2]; % Creates a column vector.
end

  • via assigning to an array index larger than the current size (again slow if done in a loop):

    % Create a vector containing the numbers 1, 4, 9, 16, ... 100.
for idx = 1 : 10
    a(idx) = idx^2;
end

    Note: I'm not sure if this works in every version of Matlab.

于 2012-07-20T20:56:55.880 に答える
4 
arr = zeros(10,1); % to initialize array
count = 0;  
for i=1:10  
arr(i) = count;  
count = count+1;    
end
于 2012-07-20T17:29:50.420 に答える
1

In order to assign a value to an array you need to tell matlab where in the array you want it to go.

First, create an array of zeros the right size with

arr = zeros(1,10);

Then you can assign count to element i of arr with

arr(i) = count;

So the code you provided becomes

count = 0;
arr = zeros(1,10);
for i=1:10
    arr(i) = count;
    count = count + 1;
end

Of course, as other people have mentioned, there are much easier ways to do this particular task, such as

arr = 0:9;

Where 0:9 is matlab shorthand for 'a row-array containing the integers zero through nine'.

于 2012-07-20T17:32:24.217 に答える