![matrix matlab matrix matlab](https://i.ytimg.com/vi/J2bjzpyW6ro/maxresdefault.jpg)
We can also determine the size along a specific dimension with size().
#Matrix matlab code#
The length() command gives the number of elements in the first non-singleton dimension, and is frequently used when the input is a row or column vector however, it can make code less readable as it fails to make the dimensionality of the input explicit. We refer to dimensions of size 1 as singleton dimensions. We can determine the size of a matrix by using the size() command = size(A)Īnd the number of elements by using the numel() command. The functions true() and false(), act just like ones() and zeros() but create logical arrays whose entries take only 1 byte each rather than 32.
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L = triu(ones(3,4)) % 3-by-4 matrix whose upper triangular part is all ones. K = tril(ones(3,4)) % 3-by-4 matrix whose lower triangular part is all ones. J = blkdiag(rand(2,2),ones(3,2)) % 5-by-4 block diagonal matrix I = logspace(0,2,6) % 1-by-6 matrix of log-spaced numbers from 10^0 to 10^2
![matrix matlab matrix matlab](https://i.ytimg.com/vi/AAskRzfcDA4/maxresdefault.jpg)
= meshgrid(1:5) % 5-by-5 grids of numbers A = zeros(4,5) % 4-by-5 matrix of all zerosī = ones (2,3) % 2-by-3 matrix of all onesĬ = rand(3,3) % 3-by-3 matrix of uniform random numbers in ĭ = randn(2,5) % 2-by-5 matrix of standard normally distributed numbers D = Īlternatively, there are several functions that will generate matrices for us. A = 1:10 % start at 1, increment by 1, stop at 10ī = 1:2:10 % start at 1, increment by 2, stop at 10Ĭ = 10:-1:3 % start at 10, decrement by 1, stop at 3 We can often exploit patterns in the entries to create matrices more succinctly. We, (and Matlab) always refer to rows first and columns second. We say that this matrix is of size 4-by-3 indicating that it has 4 rows and 3 columns. Entries on each row are separated by a space or comma and rows are separated by semicolons, (or newlines). We begin by simply entering data directly. But sum(sum(A)) requires that you know the dimension of your array is 2.There are a number of ways to create a matrix in Matlab. I tried the largest size allowed on my computer a few more times. So if you have similar experience with Matlab timers, none of the tests can discern sum(A(:)) and sum(sum(A)). In my experience, both timers are only meaningful up to. The cputime for sum(sum(A)) in seconds is In each test, A=rand(size) and size is specified in the displayed texts. It is likely that they hard-code sum(sum(A)) to be a single loop, the same to sum(A(:)).īelow I offer some testing results. But I think sum(sum(A)) is very wide-spread amongst users. It would be slower if Matlab actually creates a row vector recording the sum of each column of A first and then sum over the columns.
![matrix matlab matrix matlab](https://i.ytimg.com/vi/dqvdgxEY33s/maxresdefault.jpg)
If it is, then we have a reason to believe that the shape of an array is not directly related to the way the data is stored and manipulated.)Īs such, there is no reason sum(sum(A)) should be faster. (One can test reshape() and check if reshaping is fast in Matlab. So the shape of A does not quite matter in sum(). In my experience, arrays in Matlab seems to be stored in a continuous block in memory as stacked column vectors. The best practice is definitely to avoid loops or recursions in Matlab.