Maximum

Find maximum values in input or sequence of inputs

Library

Statistics

dspstat3

Description

The Maximum block identifies the value and/or position of the largest element in each row or column of the input, along vectors of a specified dimension of the input, or of the entire input. The Maximum block can also track the maximum 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.

The Maximum block supports real and complex floating-point, fixed-point, and Boolean inputs. Real fixed-point inputs can be either signed or unsigned, while complex fixed-point inputs must be signed. The data type of the maximum values output by the block match the data type of the input. The index values output by the block are double when the input is double, and uint32 otherwise.

For the Value, Index, and Value and Index modes, the Maximum block produces identical results as the MATLAB® max function when it is called as [y I] = max(u,[],D), where u and y are the input and output, respectively, D is the dimension, and I is the index.

Value Mode

When the Mode parameter is set to Value, the block computes the maximum value in each row or column of the input, along vectors of a specified dimension of the input, or of the entire input at each sample time, and outputs the array y. Each element in y is the maximum value in the corresponding column, row, vector, or entire input. The output y depends on the setting of the Find the maximum value over parameter. For example, consider a 3-dimensional input signal of size M-by-N-by-P:

  • Each row — The output at each sample time consists of an M-by-1-by-P array, where each element contains the maximum value of each vector over the second dimension of the input. For an input that is an M-by-N matrix, the output at each sample time is an M-by-1 column vector.

  • Each column — The output at each sample time consists of a 1-by-N-by-P array, where each element contains the maximum value of each vector over the first dimension of the input. For an input that is an M-by-N matrix, the output at each sample time is a 1-by-N row vector.

    In this mode, the block treats length-M unoriented vector inputs as M-by-1 column vectors.

  • Entire input — The output at each sample time is a scalar that contains the maximum value in the M-by-N-by-P input matrix.

  • Specified dimension — The output at each sample time depends on Dimension. If Dimension is set to 1, the output is the same as that when you select Each column. If Dimension is set to 2, the output is the same as when you select Each row. If Dimension is set to 3, the output at each sample time is an M-by-N matrix containing the maximum value of each vector over the third dimension of the input.

For complex inputs, the block selects the value in each row or column of the input, along vectors of a specified dimension of the input, or of the entire input that has the maximum magnitude squared as shown below. For complex value u=a+bi, the magnitude squared is a2+b2.

Index Mode

When Mode is set to Index, the block computes the maximum value in each row or column of the input, along vectors of a specified dimension of the input, or of the entire input, and outputs the index array I. Each element in I is an integer indexing the maximum value in the corresponding column, row, vector, or entire input. The output I depends on the setting of the Find the maximum value over parameter. For example, consider a 3-dimensional input signal of size M-by-N-by-P:

  • Each row — The output at each sample time consists of an M-by-1-by-P array, where each element contains the index of the maximum value of each vector over the second dimension of the input. For an input that is an M-by-N matrix, the output at each sample time is an M-by-1 column vector.

  • Each column — The output at each sample time consists of a 1-by-N-by-P array, where each element contains the index of the maximum value of each vector over the first dimension of the input. For an input that is an M-by-N matrix, the output at each sample time is a 1-by-N row vector.

    In this mode, the block treats length-M unoriented vector inputs as M-by-1 column vectors.

  • Entire input — The output at each sample time is a 1-by-3 vector that contains the location of the maximum value in the M-by-N-by-P input matrix. For an input that is an M-by-N matrix, the output will be a 1-by-2 vector.

  • Specified dimension — The output at each sample time depends on Dimension. If Dimension is set to 1, the output is the same as when you select Each column. If Dimension is set to 2, the output is the same as when you select Each row. If Dimension is set to 3, the output at each sample time is an M-by-N matrix containing the indices of the maximum values of each vector over the third dimension of the input.

When a maximum value occurs more than once, the computed index corresponds to the first occurrence. For example, when the input is the column vector [3 2 1 2 3]', the computed one-based index of the maximum value is 1 rather than 5 when Each column is selected.

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.

Value and Index Mode

When Mode is set to Value and Index, the block outputs both the maxima and the indices.

Running Mode

When Mode is set to Running, the block tracks the maximum value of each channel in a time sequence of M-by-N inputs. In this mode, you must also specify a value for the Input processing parameter:

  • When you select Elements as channels (sample based), the block outputs an M-by-N array. Each element yij of the output contains the maximum value observed in element uij for all inputs since the last reset.

  • When you select Columns as channels (frame based), the block outputs an M-by-N matrix. Each element yij of the output contains the maximum value observed in the jth column of all inputs since the last reset, up to and including element uij of the current input.

Running Mode for Variable-Size Inputs

When your inputs are of variable size, and you set the Mode to Running , there are two options:

  • If you set the Input processing parameter to Elements as channels (sample based), the state is reset.

  • If you set the Input processing parameter to Columns as channels (frame based), then there are two cases:

    • When the input size difference is in the number of channels (i.e., number of columns), the state is reset.

    • When the input size difference is in the length of channels (i.e., number of rows), there is no reset and the running operation is carried out as usual.

Resetting the Running Maximum

The block resets the running maximum whenever a reset event is detected at the optional Rst port. The reset sample time must be a positive integer multiple of the input sample time.

When a reset event occurs while the Input processing parameter is set to Elements as channels (sample based), the running maximum for each channel is initialized to the value in the corresponding channel of the current input. Similarly, when the Input processing parameter is set to Columns as channels (frame based), the running maximum for each channel is initialized to the earliest value in each channel of the current input.

You specify the reset event in the Reset port menu:

  • 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, reset signals have a one-sample latency. Therefore, when the block detects a reset event, there is a one-sample delay at the reset port rate before the block applies the reset. For more information on latency and the Simulink tasking modes, see Excess Algorithmic Delay (Tasking Latency) and Scheduling in the Simulink Coder™ User's Guide.

ROI Processing

To calculate the statistical value within a particular region of interest (ROI) of the input, select the Enable ROI processing check box. This applies to any mode other than running mode and when you set the Find the maximum value over parameter to Entire input and you select the Enable ROI processing check box. ROI processing applies only for 2-D inputs.

    Note:   Full ROI processing is available only if you have a Computer Vision System Toolbox™ license. If you do not have a Computer Vision System Toolbox license, you can still use ROI processing, but are limited to the ROI type Rectangles.

Use the ROI type parameter to specify whether the ROI is a rectangle, line, label matrix, or binary mask. A binary mask is a binary image that enables you to specify which pixels to highlight, or select. In a label matrix, pixels equal to 0 represent the background, pixels equal to 1 represent the first object, pixels equal to 2 represent the second object, and so on. When the ROI type parameter is set to Label matrix, the Label and Label Numbers ports appear on the block. Use the Label Numbers port to specify the objects in the label matrix for which the block calculates statistics. The input to this port must be a vector of scalar values that correspond to the labeled regions in the label matrix. For more information about the format of the input to the ROI port when the ROI is a rectangle or a line, see the Draw Shapes block reference page.

For rectangular ROIs, use the ROI portion to process parameter to specify whether to calculate the statistical value for the entire ROI or just the ROI perimeter.

Use the Output parameter to specify the block output. The block can output separate statistical values for each ROI or the statistical value for all specified ROIs. This parameter is not available if, for the ROI type parameter, you select Binary mask.

If, for the ROI type parameter, you select Rectangles or Lines, the Output flag indicating if ROI is within image bounds check box appears in the dialog box. If you select this check box, the Flag port appears on the block. The following tables describe the Flag port output based on the block parameters.

Output = Individual statistics for each ROI

Flag Port OutputDescription
0ROI is completely outside the input image.
1ROI is completely or partially inside the input image.

Output = Single statistic for all ROIs

Flag Port OutputDescription
0All ROIs are completely outside the input image.
1At least one ROI is completely or partially inside the input image.

If the ROI is partially outside the image, the block only computes the statistical values for the portion of the ROI that is within the image.

If, for the ROI type parameter, you select Label matrix, the Output flag indicating if input label numbers are valid check box appears in the dialog box. If you select this check box, the Flag port appears on the block. The following tables describe the Flag port output based on the block parameters.

Output = Individual statistics for each ROI

Flag Port OutputDescription
0Label number is not in the label matrix.
1Label number is in the label matrix.

Output = Single statistic for all ROIs

Flag Port OutputDescription
0None of the label numbers are in the label matrix.
1At least one of the label numbers is in the label matrix.

Fixed-Point Data Types

The parameters on the Data Types pane of the block dialog are only used for complex fixed-point inputs. The sum of the squares of the real and imaginary parts of such an input are formed before a comparison is made, as described in Value Mode. The results of the squares of the real and imaginary parts are placed into the product output data type. The result of the sum of the squares is placed into the accumulator data type. These parameters are ignored for other types of inputs.

Examples

In the following ex_maximum_refex_maximum_ref model, the Maximum block calculates the running maximum of a 3-by-2 matrix input, dsp_examples_u. The Input processing parameter is set to Columns as channels (frame based), so the block processes the input as a two channel signal with a frame size of three. The running maximum is reset at t=2 by an impulse to the block's Rst port.

The operation of the block is shown in the following figure.

Dialog Box

The Main pane of the Maximum block dialog appears as follows.

Mode

Specify the block's mode of operation:

  • Value — Output the maximum value of each input

  • Index — Output the index of the maximum value

  • Value and index — Output both the value and the index

  • Running — Track the maximum value of the input sequence over time

For more information, see Description.

Input processing

Specify how the block should process the input when computing the running maximum. You can set this parameter to one of the following options:

  • Columns as channels (frame based) — When you select this option, the block treats each column of the input as a separate channel.

  • Elements as channels (sample based) — When you select this option, the block treats each element of the input as a separate channel.

This parameter appears only when you set the Mode to Running.

    Note:   The option Inherit from input (this choice will be removed - see release notes) will be removed in a future release. See Frame-Based Processing in the DSP System Toolbox™ Release Notes for more information.

Index base

Specify whether the index of the maximum value is reported using one-based or zero-based numbering. This parameter is only visible when the Mode parameter is set to Index or Value and index.

Find the maximum value over

Specify whether to find the maximum value along rows, columns, entire input, or the dimension specified in the Dimension parameter. For more information, see Description.

Treat sample-based row input as a column

Select to treat sample-based length-M row vector inputs as M-by-1 column vectors. This parameter is only visible when the Find the maximum value of parameter is set to Each column.

Reset port

Specify the reset event that causes the block to reset the running maximum. The sample time of the input to the Rst port must be a positive integer multiple of the input sample time. This parameter appears only when you set the Mode parameter to Running. For information about the possible values of this parameter, see Resetting the Running Maximum.

Dimension

Specify the dimension (one-based value) of the input signal, over which the maximum is computed. The value of this parameter cannot exceed the number of dimensions in the input signal. This parameter is only visible when the Find the maximum value over parameter is set to Specified dimension.

Enable ROI processing

Select this check box to calculate the statistical value within a particular region of each image. This parameter appears only when you set the Find the maximum value over parameter to Entire input, and the block is not in running mode.

    Note:   Full ROI processing is available only if you have a Computer Vision System Toolbox license. If you do not have a Computer Vision System Toolbox license, you can still use ROI processing, but are limited to the ROI type Rectangles.

The ROI processing parameters appear on the dialog box as follows.

ROI type

Specify the type of ROI you want to use. Your choices are Rectangles, Lines, Label matrix, or Binary mask.

ROI portion to process

Specify whether you want to calculate the statistical value for the entire ROI or just the ROI perimeter. This parameter appears only if you specify an ROI type of Rectangles.

Output

Specify the block output. The block can output a vector of separate statistical values for each ROI or a scalar value that represents the statistical value for all the specified ROIs. This parameter is not available if, for the ROI type parameter, you select Binary mask.

Output flag

Output flag indicating if ROI is within image bounds

Output flag indicating if label numbers are valid

When you select either of these check boxes, the Flag port appears on the block. For a description of the Flag port output, see the tables in ROI Processing.

The Output flag indicating if ROI is within image bounds check box is only visible when you select Rectangles or Lines as the ROI type.

The Output flag indicating if label numbers are valid check box is only visible when you select Label matrix for the ROI type parameter.

The Data Types pane of the Maximum block dialog appears as follows.

    Note:   The parameters on the Data Types pane are only used for complex fixed-point inputs. The sum of the squares of the real and imaginary parts of such an input are formed before a comparison is made, as described in Value Mode. The results of the squares of the real and imaginary parts are placed into the product output data type. The result of the sum of the squares is placed into the accumulator data type. These parameters are ignored for other types of inputs.

Rounding mode

Select the rounding mode for fixed-point operations.

Overflow mode

Select the overflow mode for fixed-point operations.

Product output data type

Specify the product output data type. See Fixed-Point Data Types and Multiplication Data Types for illustrations depicting the use of the product output data type in this block. You can set it to:

  • A rule that inherits a data type, for example, Inherit: Same as input

  • An expression that evaluates to a valid data type, for example, fixdt([],16,0)

Click the Show data type assistant button to display the Data Type Assistant, which helps you set the Product output data type parameter.

See Specify Data Types Using Data Type Assistant for more information.

Accumulator data type

Specify the accumulator data type. See Fixed-Point Data Types for illustrations depicting the use of the accumulator data type in this block. You can set this parameter to:

  • A rule that inherits a data type, for example, Inherit: Same as product output

  • An expression that evaluates to a valid data type, for example, fixdt([],16,0)

Click the Show data type assistant button to display the Data Type Assistant, which helps you set the Accumulator data type parameter.

See Specify Data Types Using Data Type Assistant for more information.

Lock data type settings against changes by the fixed-point tools

Select this parameter to prevent the fixed-point tools from overriding the data types you specify on the block mask.

HDL Code Generation

This block supports HDL code generation using HDL Coder™. HDL Coder provides additional configuration options that affect HDL implementation and synthesized logic. For more information on implementations, properties, and restrictions for HDL code generation, see Maximum.

Supported Data Types

PortSupported Data Types

Input

  • Double-precision floating point

  • Single-precision floating point

  • Fixed point (signed and unsigned)

  • Boolean

  • 8-, 16-, and 32-bit signed integers

  • 8-, 16-, and 32-bit unsigned integers

Reset

  • Double-precision floating point

  • Single-precision floating point

  • Boolean

  • 8-, 16-, and 32-bit signed integers

  • 8-, 16-, and 32-bit unsigned integers

Idx

  • Double-precision floating point

  • 32-bit unsigned integers

Val

  • Double-precision floating point

  • Single-precision floating point

  • Fixed point (signed and unsigned)

  • Boolean

  • 8-, 16-, and 32-bit signed integers

  • 8-, 16-, and 32-bit unsigned integers

See Also

MeanDSP System Toolbox
MinimumDSP System Toolbox
MinMaxSimulink
maxMATLAB
dsp.MaximumDSP System Toolbox

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