DSP Blockset

Variable Selector

Select a subset of rows or columns from the input.

Library

Signal Management / Indexing

Description

The Variable Selector block extracts a subset of rows or columns from the M-by-N input matrix at the In port, u.

When the Select parameter is set to Rows, the Variable Selector block extracts rows from the input matrix, while if the Select parameter is set to Columns, the block extracts columns.

When the Selector mode parameter is set to Variable, the length-L vector input to the Idx port selects L rows or columns of u to pass through to the output. The elements of the indexing vector can be updated at each sample time, but the vector length must remain the same throughout the simulation.

When the Selector mode parameter is set to Fixed, the Idx port is disabled, and the length-L vector specified in the Elements parameter selects L rows or columns of u to pass through to the output. The Elements parameter is tunable, so you can change the values of the indexing vector elements at any time during the simulation; however, the vector length must remain the same.

For both variable and fixed indexing modes, the row selection operation is equivalent to

• y = u(idx,:)             % Equivalent MATLAB code
  

and the column selection operation is equivalent to

• y = u(:,idx)             % Equivalent MATLAB code
  

where idx is the length-L indexing vector. The row selection output size is L-by-N and the column selection output size is M-by-L. Input rows or columns can appear any number of times in the output, or not at all.

When the input is a 1-D vector, the Select parameter is ignored; the output is a 1-D vector of length L containing those elements specified by the length-L indexing vector.

When an element of the indexing vector references a nonexistent row or column of the input, the block reacts with the behavior specified by the Invalid index parameter. The following options are available:

• Clip index -- Clip the index to the nearest valid value, and do not issue an alert. Example: For a 64-by-N input, an index of 72 is clipped to 64; an index of -2 is clipped to 1.
• Clip and warn -- Display a warning message in the MATLAB command window, and clip as above.
• Generate error -- Display an error dialog box and terminate the simulation.

Note    The Variable Selector block always copies the selected input rows to a contiguous block of memory (unlike the Simulink Selector block).

Dialog Box

Select

The dimension of the input to select, Rows or Columns. Tunable.

Selector mode

The type of indexing operation to perform, Variable or Fixed. Variable indexing uses the input at the Idx port to select rows or columns from the input at the In port. Fixed indexing uses the Elements parameter value to select rows from the input at the In port, and disables the Idx port.

Elements

A vector containing the indices of the input rows or columns that will appear in the output matrix. This parameter is available when Fixed is selected in the Selector mode parameter. Tunable.

Index mode

When set to One-based, an index value of 1 refers to the first row or column of the input. When set to Zero-based, an index value of 0 refers to the first row or column of the input.

Invalid index

Response to an invalid index value. Tunable.

Supported Data Types

• Double-precision floating point
• Single-precision floating point
• Fixed-point
• Custom data types
• Boolean
• 8-, 16-, and 32-bit signed integers
• 8-, 16-, and 32-bit unsigned integers

To learn how to convert to the above data types in MATLAB and Simulink, see Supported Data Types and How to Convert to Them.

See Also

Multiport Selector	DSP Blockset
Permute Matrix	DSP Blockset
Selector	Simulink
Submatrix	DSP Blockset

Also see Indexing for a list of all the blocks in the Indexing library.

Variable Integer Delay

Variance