DSP Blockset

Minimum

Find the minimum values in an input or sequence of inputs.

Library

Statistics

Description

The Minimum block identifies the value and position of the smallest element in each column of the input, or tracks the minimum values in a sequence of inputs over a period of time. The Mode parameter specifies the block's mode of operation, and can be set to Value, Index, Value and Index, or Running.

Value Mode

When Mode is set to Value, the block computes the minimum value in each column of the M-by-N input matrix u independently at each sample time.

• val = min(u)         % Equivalent MATLAB code
  

For convenience, length-M 1-D vector inputs and sample-based length-M row vector inputs are both treated as M-by-1 column vectors.

The output at each sample time, val, is a 1-by-N vector containing the minimum value of each column in u. For complex inputs, the block selects the value in each column that has the minimum magnitude, min(abs(u)), as shown below.

The frame status of the output is the same as that of the input.

Index Mode

When Mode is set to Index, the block computes the minimum value in each column of the M-by-N input matrix u,

• [val,idx] = min(u)       % Equivalent MATLAB code
  

and outputs the sample-based 1-by-N index vector, idx. Each value in idx is an integer in the range [1 M] indexing the minimum value in the corresponding column of u. When inputs to the block are double-precision values, the index values are double-precision values. Otherwise, the index values are 32-bit unsigned integer values.

As in Value mode, length-M 1-D vector inputs and sample-based length-M row vector inputs are both treated as M-by-1 column vectors.

If a minimum value occurs more than once in a particular column of u, the computed index corresponds to the first occurrence. For example, if the input is the column vector [-1 2 3 2 -1]', the computed index of the minimum value is 1 rather than 5.

Value and Index Mode

When Mode is set to Value and Index, the block outputs both the vector of minima, val, and the vector of indices, idx.

Running Mode

When Mode is set to Running, the block tracks the minimum value of each channel in a time-sequence of M-by-N inputs. For sample-based inputs, the output is a sample-based M-by-N matrix with each element y_ij containing the minimum value observed in element u_ij for all inputs since the last reset. For frame-based inputs, the output is a frame-based M-by-N matrix with each element y_ij containing the minimum value observed in the jth column of all inputs since the last reset, up to and including element u_ij of the current input.

As in the other modes, length-M 1-D vector inputs and sample-based length-M row vector inputs are both treated as M-by-1 column vectors.

Resetting the Running Minimum.   The block resets the running minimum whenever a reset event is detected at the optional Rst port. The rate of the reset signal must be a positive integer multiple of the rate of the data signal input.

When the block is reset for sample-based inputs, the running minimum for each channel is initialized to the value in the corresponding channel of the current input. For frame-based inputs, the running minimum for each channel is initialized to the earliest value in each channel of the current input.

The reset event is specified by the Reset port parameter, and can be one of the following:

• None disables the Rst port.
• Rising edge -- Triggers a reset operation when the Rst input does one of the following:
• Rises from a negative value to a positive value or zero
• Rises from zero to a positive value, where the rise is not a continuation of a rise from a negative value to zero (see the following figure)
  
  
• Falling edge -- Triggers a reset operation when the Rst input does one of the following:
• Falls from a positive value to a negative value or zero
• Falls from zero to a negative value, where the fall is not a continuation of a fall from a positive value to zero (see the following figure)
  
  
• Either edge -- Triggers a reset operation when the Rst input is a Rising edge or Falling edge (as described above).
• Non-zero sample -- Triggers a reset operation at each sample time that the Rst input is not zero.

Note    When running simulations in the Simulink MultiTasking mode, sample-based reset signals have a one-sample latency, and frame-based reset signals have one frame of latency. Thus, there is a one-sample or one-frame delay between the time the block detects a reset event, and when it applies the reset. For more information on latency and the Simulink tasking modes, see Excess Algorithmic Delay (Tasking Latency) and the topic on the Simulation Parameters dialog box in the Simulink documentation.

Example

The Minimum block in the model below calculates the running minimum of a frame-based 3-by-2 (two-channel) matrix input. The running minimum is reset at t=2 by an impulse to the block's Rst port.

The Minimum block has the following settings:

• Mode = Running
• Reset port = Non-zero sample

The Signal From Workspace block has the following settings:

• Signal = u
• Sample time = 1/3
• Samples per frame = 3

where

• u = [6 1 3 -7 2 5 8 0 -1 -3 2 1;1 3 9 2 4 2 6 2 5 0 4 17]'
  

The Discrete Impulse block has the following settings:

• Delay (samples) = 2
• Sample time = 1
• Samples per frame = 1

The block's operation is shown in the figure below.

Dialog Box

Mode

The block's mode of operation: Output the minimum value of each input (Value), the index of the minimum value (Index), both the value and the index (Value and Index), or track the minimum values in the input sequence over time (Running).

Reset port

Determines the reset event that causes the block to reset the running minimum. The rate of the reset signal must be a positive integer multiple of the rate of the data signal input. This parameter is enabled only when you set the Mode parameter to Running. For more information, see Resetting the Running Minimum.

Supported Data Types

• Double-precision floating point
• Single-precision floating point
• Fixed-point
• Boolean -- The block accepts Boolean inputs to the Rst port.
• 32-bit unsigned integer -- When inputs to the block are double-precision values, the index values are double-precision values. Otherwise, the index values are 32-bit unsigned integer values.

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

Maximum	DSP Blockset
Mean	DSP Blockset
MinMax	Simulink
Histogram	DSP Blockset
min	MATLAB

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

Median

Modified Covariance AR Estimator