MAX Maximum Function
Section: Elementary Functions
UsageComputes the maximum of an array along a given dimension, or alternately, computes two arrays (entry-wise) and keeps the smaller value for each array. As a result, the
maxfunction has a number of syntaxes. The first one computes the maximum of an array along a given dimension. The first general syntax for its use is either
[y,n] = max(x,,d)
x is a multidimensional array of numerical type, in which case the
y is the maximum of
x along dimension
The second argument
n is the index that results in the maximum.
In the event that multiple maxima are present with the same value,
the index of the first maximum is used.
The second general syntax for the use of the
max function is
[y,n] = max(x)
In this case, the maximum is taken along the first non-singleton
x. For complex data types,
the maximum is based on the magnitude of the numbers. NaNs are
ignored in the calculations.
The third general syntax for the use of the
max function is as
a comparison function for pairs of arrays. Here, the general syntax is
y = max(x,z)
z are either both numerical arrays of the same dimensions,
or one of the two is a scalar. In the first case, the output is the
same size as both arrays, and is defined elementwise by the smaller of the
two arrays. In the second case, the output is defined elementwise by the
smaller of the array entries and the scalar.
Function InternalsIn the general version of the
maxfunction which is applied to a single array (using the
max(x)syntaxes), The output is computed via
and the output array
n of indices is calculated via
In the two-array version (
max(x,z)), the single output is computed as
ExampleThe following piece of code demonstrates various uses of the maximum function. We start with the one-array version.
--> A = [5,1,3;3,2,1;0,3,1] A = 5 1 3 3 2 1 0 3 1
We first take the maximum along the columns, resulting in a row vector.
--> max(A) ans = 5 3 3
Next, we take the maximum along the rows, resulting in a column vector.
--> max(A,,2) ans = 5 3 3
When the dimension argument is not supplied,
max acts along the first non-singular dimension. For a row vector, this is the column direction:
--> max([5,3,2,9]) ans = 9
For the two-argument version, we can compute the smaller of two arrays, as in this example:
--> a = int8(100*randn(4)) a = 8 127 -51 -57 -5 -25 -62 -14 -17 -73 127 -73 -102 21 36 39 --> b = int8(100*randn(4)) b = 59 127 46 24 -98 -78 -50 -114 -128 57 127 -2 -64 -95 30 127 --> max(a,b) ans = 59 127 46 24 -5 -25 -50 -14 -17 57 127 -2 -64 21 36 127
Or alternately, we can compare an array with a scalar
--> a = randn(2) a = 1.4356 0.4894 -0.8816 0.6359 --> max(a,0) ans = 1.4356 0.4894 0 0.6359