MATLAB Arrays as Python Variables - MATLAB & Simulink (original) (raw)

The matlab Python® module provides array classes to represent arrays of MATLAB® numeric types as Python variables so that MATLAB arrays can be passed between Python and MATLAB.

MATLAB Classes in the matlab.engine Python Module

You can use MATLAB numeric arrays in Python code by importing the matlab.engine Python package and calling the necessary constructors. For example:

import matlab.engine a = matlab.double([[1, 2, 3],[4, 5, 6]])

The name of the constructor indicates the MATLAB numeric type. You can pass MATLAB arrays as input arguments to MATLAB functions called from Python. When a MATLAB function returns a numeric array as an output argument, the array is returned to Python.

You can customize the array constructors as follows:

• You can initialize an array with an optional initializer input argument that contains numbers. The initializer argument, which is the first positional argument, must be a Python sequence type such as a list,tuple, or range. You can specifyinitializer to contain multiple sequences of numbers.
• You can initialize an array with an optional vector input argument that contains input of size 1-by-N. If you use vector, you cannot use initializer.
  Note
  When the input is of size 1-by-N, using vector is more efficient than using initializer. Python always knows the length of a one-dimensional sequence, and it can use this information to perform a single allocation of the array that will hold the output.
• You can create a multidimensional array using one of the following options:
  • Specify a nested sequence without specifying the size.
  • Specify a nested sequence and also specify a size input argument that matches the dimensions of the nested sequence.
  • Specify a one-dimensional sequence together with a multidimensional size. In this case, the sequence is assumed to represent the elements in column-major order.
• You can create a MATLAB array of complex numbers by setting the optionalis_complex input argument to True.
• You can use custom types to create MATLAB arrays in Python. The custom type must implement the Python buffer protocol. One example is ndarray in NumPy.

You can create MATLAB arrays using these classes:

Properties and Methods of MATLAB Classes in the matlab Python Package

All MATLAB arrays created with matlab.engine package constructors have the following properties and methods:

Properties

Methods

Multidimensional MATLAB Arrays in Python

In Python, you can create multidimensional MATLAB arrays of any numeric type. Use two Pythonlist variables to create a 2-by-5 MATLAB array of doubles.

import matlab.engine
A = matlab.double([[1,2,3,4,5], [6,7,8,9,10]])
print(A)

[[1.0,2.0,3.0,4.0,5.0],[6.0,7.0,8.0,9.0,10.0]]

The size attribute of A shows that it is a 2-by-5 array.

Index Into MATLAB Arrays in Python

You can index into MATLAB arrays just as you can index into Pythonlist and tuple variables.

import matlab.engine
A = matlab.int8([1,2,3,4,5])
print(A[0])

The size of the MATLAB array is (1,5); therefore, A[0] is [1,2,3,4,5]. Index into the array to get 3.

Python indexing is zero-based. When you access elements of MATLAB arrays in a Python session, use zero-based indexing.

Index into a multidimensional MATLAB array.

A = matlab.double([[1,2,3,4,5], [6,7,8,9,10]])
print(A[1][2])

Slice MATLAB Arrays in Python

You can slice MATLAB arrays the same way you slice Pythonlist and tuple variables.

import matlab.engine
A = matlab.int8([[1,2,3,4,5]])
print(A[0][1:4])

You can assign data to a slice. This code shows assignment from a Pythonlist to a slice of an array.

A = matlab.double([[1,2,3,4],[5,6,7,8]]);
A[0] = [10,20,30,40]
print(A)

[[10.0,20.0,30.0,40.0],[5.0,6.0,7.0,8.0]]

You can assign data from another MATLAB array, or from any Python iterable that contains numbers.

You can specify slices for assignment as shown here.

A = matlab.int8([1,2,3,4,5,6,7,8]);
A[0][2:4] = [30,40]
A[0][6:8] = [70,80]
print(A)

Reshape MATLAB Arrays in Python

You can reshape a MATLAB array in Python with the reshape method. Input argumentsize must be a sequence that preserves the number of elements. Use reshape to change a 1-by-9 MATLAB array to 3-by-3.

import matlab.engine
A = matlab.int8([1,2,3,4,5,6,7,8,9])
A.reshape((3,3))
print(A)

[[1,4,7],[2,5,8],[3,6,9]]

See Also

Topics

• Use MATLAB Arrays in Python