7 Sep 2011 All entries of matlab array except certain index. Say you have a matrix D: D = [1 2 3 4 5];. And you want to be able to suck out all entries that are I think to use "randint" to regenerate indexes then create new vector using new index order. But problem is such a random indexing may repeated The two indices vectors i and j contains redundant information. We can compress the column index vector j to a column pointer vector with length n + 1. The value j 25 Nov 2015 A matrix is a convenient way to store an array of numbers. Use indices when you want to extract values from a non-rectangular pattern. populate the appropriate fields of the model struct using standard MATLAB routines. Note that all vector fields within the model variable must be dense vectors constraint are specified by placing their indices in vector model.sos(i). index. MATLAB extracts the matrix elements corresponding to the nonzero values of the logical array. The output is always in the form of a column vector. For example, A(A > 12) extracts all the elements of A that are greater than 12.
If you try to refer to elements outside an array on the right side of an assignment statement, MATLAB throws an error. test = A(4,5). Index exceeds matrix The result is a column vector of linear indices. Each index describes the location of an element in A that is less than 9, so in practice A(I) returns the same
Array Indexing. Open Live Script. Every variable in MATLAB® is an array that can hold many numbers. When you want to access selected elements of an array, use indexing. For example, consider the 4-by-4 magic square A: A = magic(4) In Octave If A = 1 3 2 6 5 4 7 9 8 1) For Each Column Max value and corresponding index of them can be found by >> [max_values,indices] =max(A,[],1) max_values = 7 9 8 indices = 3 3 3 2) For Each Row Max value and corresponding index of them can be found by >> [max_values,indices] =max(A,[],2) max_values = 3 6 9 indices = 2 1 2 Similarly For minimum value >> [min_values,indices] =min(A,[],1) min_values = 1 3 2 indices = 1 1 1 >> [min_values,indices] =min(A,[],2) min_values = 1 4 7 indices Indexing vectors and arrays in Matlab. There are times where you have a lot of data in a vector or array and you want to extract a portion of the data for some analysis. For example, maybe you want to plot column 1 vs column 2, or you want the integral of data between x = 4 and x = 6, but your vector covers 0 < x < 10. But in MATLAB each element of an array can be indexed by a so-called linear index, too. This increases in the following way – the linear index is in superscript: A = \left[\begin{matrix}1^1 & 6^5 & 7^9 & 8^{13} & 2^{17} \\ 1^2 & 5^6 & 6^{10} & 7^{14} & 3^{18} \\ 1^3 & 8^7 & 9^{11} & 2^{15} & 3^{19} \\ 0^4 & 5^8 & 2^{12} & 9^{16} & 9^{20}\end{matrix}\right] Position of an element in a vector. Learn more about vector MATLAB. Skip to content. Position of an element in a vector. Follow 2.096 views (last 30 days) F.O on 18 Oct 2017. Vote. 1 ⋮ Also note that if you are then going to use this index for indexing into the array, it's usually more efficient to just use the logical array to index How can I index a MATLAB array returned by a function without first assigning it to a local variable? Ask Question Asked 9 years, However, MATLAB complains about Unbalanced or unexpected parenthesis or bracket on the first parenthesis before the 3. How to index an array value in a MATLAB-Function in Simulink? 2.
Note that when you give a multi-dimensional array as the index into an array (as in the last line of the table above), Matlab will usually convert it to a column vector (it will automatically convert repmatIdx into repmatIdx(:)), except when only one index is provided. When only one index is provided, it will index according to the structure of the multi-dimensional array. Linear Indices. A linear index allows use of a single subscript to index into an array, such as A(k). MATLAB ® treats the array as a single column vector with each column appended to the bottom of the previous column. Thus, linear indexing numbers the elements in the columns from top to bottom, left to right. A (j:k) uses the vector j:k to index into A and is therefore equivalent to the vector [A (j), A (j+1), , A (k)]. A (:,j:k) includes all subscripts in the first dimension but uses the vector j:k to index in the second dimension. This returns a matrix with columns [A (:,j), A (:,j+1), , A (:,k)]. Vectors In MATLAB a vector is a matrix with either one row or one column. The distinction between row vectors and column vectors is essential.Many programming errors are caused by using a row vector where a column vector is required, and vice versa. I think at one stage we have the same index, mine was “b2(:,3,:)>5” and yours was “c = b(:,3,:)” followed by “(c > 5) = -100”. They then both obtain the same index values; >> ind Indexing Arrays. Indexing into Matlab arrays is very often glossed over, but it is actually quite a powerful (and fast) technique. There are a surprising number of things that can be done by just indexing into a Matlab array. These indexing tricks come in handy to avoid "for" loops and in vectorizing code.
In Octave If A = 1 3 2 6 5 4 7 9 8 1) For Each Column Max value and corresponding index of them can be found by >> [max_values,indices] =max(A,[],1) max_values = 7 9 8 indices = 3 3 3 2) For Each Row Max value and corresponding index of them can be found by >> [max_values,indices] =max(A,[],2) max_values = 3 6 9 indices = 2 1 2 Similarly For minimum value >> [min_values,indices] =min(A,[],1) min_values = 1 3 2 indices = 1 1 1 >> [min_values,indices] =min(A,[],2) min_values = 1 4 7 indices