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From Workspace - Read data from workspace

Library

Sources

Description

The From Workspace block reads data from a workspace and outputs the data as a signal. The block's Data parameter specifies the workspace data using a MATLAB expression that evaluates to one of the following:

A two-dimensional matrix:
- The first element of each matrix row is a time stamp.
- The rest of each row is a scalar or vector of signal values.
The leftmost element of each row is the time stamp of the value(s) in the rest of the row.
A structure in Structure with Time format, which contains:
- A vector named time, which contains time stamps
- An array or matrix named signals.values, which contains scalars or vectors of signal values.
The n'th time element is the time stamp of the n'th signals.values element. See Importing Data from a Workspace for a description of Structure with Time format.
A Simulink.Timeseries object.

The From Workspace icon displays the expression specified in the Data parameter. The Simulink software evaluates this expression as described in Resolving Symbols.

The format of a matrix or structure read by a From Workspace block is the same as that used to load root-level input port data from the workspace. You must use the Structure with Time format or a time series object to load matrix (2-D) data from the workspace. See Importing Data from a Workspace for guidelines on choosing time vectors for discrete systems. See the documentation of the sim command for some data import capabilities that are available only for programmatic simulation.

Limitation: You cannot use a From Workspace block to import fixed-point data that is contained in a structure. Consider using a Simulink.Timeseries object instead of a structure.

Using Data Saved by a To File Block

The From Workspace block requires data written by the To File block to be transposed before the From Workspace block can read it. The source file contains consecutive time stamps at the beginnings of columns, followed by the corresponding data. The transposed data contains consecutive time stamps at the beginning of rows, followed by the corresponding data. To provide the required format, use MATLAB commands to load and transpose (') the MAT-file (see Reshaping a Matrix). You can then use a From Workspace block to access the data loaded into the workspace. Resave the transposed data if needed to avoid retransposing it again later.

Using Data Saved by a To Workspace Block

The From Workspace block requires data written by a To Workspace block to be written in Structure with Time format. Use this format to save sample-based data if you intend to use a From Workspace block to read the data back into another simulation. See Importing Data from a Workspace for a description of Structure with Time format.

Limitation: You cannot use a From Workspace block to import fixed-point data that is contained in a structure. Consider using a Simulink.Timeseries object instead of a structure.

Interpolating Missing Data Values

If you select the Interpolate data option, the block uses linear Lagrangian interpolation to compute data values for time steps that occur between time steps for which the workspace supplies data. In particular, the block linearly interpolates a missing data point from the two known data points between which it falls. For example, suppose the block reads the following time series from the workspace:

time:      1   2   3    4
signal:   253 254  ?  256

The block would output:

time:      1   2   3    4
signal:   253 254 255  256

If you clear the Interpolate data option, the block uses the most recent data value supplied from the workspace to provide any missing data values. For example, the result of the incomplete set of signal values shown above would be:

time:      1   2   3    4
signal:   253 254 254  256

Interpolating Integer Data

If the input data type is an integer type and an interpolated data point exceeds the data type's range, the block sets the missing data point to be the maximum value that the data type can represent. Similarly, if the interpolated or extrapolated value is less than the minimum value that the data type can represent, the block sets the missing data point to the minimum value that the data type can represent. For example, suppose that the data type is uint8 and the value interpolated for a missing data point is 256.

time:      1   2   3   4
signal:   253 254 255  ?

In this case, the block sets the value of the missing point to 255, the largest value that can be represented by the uint8 data type:

time:      1   2   3    4
signal:   253 254 255  255

Interpolating Boolean Data

If the input data is boolean, the block uses the value of the nearest workspace data point as the value of missing data point when determining missing data points that fall between the first and last known points. For example, suppose the workspace supplies values at time steps 1 and 4 but not at 2 and 3:

time:     1 2 3 4
signal:   1 ? ? 0

In this case, the block would use the value of data point 1 as the value of data point 2 and the value of data point 4 as the value of data point 3:

time:     1 2 3 4
signal:   1 1 0 0

The block uses the value of the last known data point as the value of time steps that occur after the last known data point.

Specifying Output After Final Data

The block's Form output after final data value by and Interpolate data parameters work together to determine the block's output after the last time step for which workspace data is available. The following table describes the block output based on the values of the two options:

Form Output Option	Interpolate Option	Block Output After Final Data
Extrapolate	On	Extrapolated from final data value
Extrapolate	Off	Error
Setting to zero	On	Zero
Setting to zero	Off	Zero
Holding final value	On	Final value from workspace
Holding final value	Off	Final value from workspace
Cyclic repetition	On	Error
Cyclic repetition	Off	Repeated from workspace if the workspace data is in structure-without-time format. Error otherwise.

For example, if Form output after final data value by is Extrapolate and Interpolate data is selected, the block uses the last two known data points to extrapolate data points that occur after the last known point. Consider the following model.

In this model, the From Workspace block reads data from the workspace consisting of the output of the Simulink Sine block sampled at one-second intervals. The workspace contains the first 16 samples of the output. The top and bottom X-Y plots display the output of the Sine Wave and From Workspace blocks, respectively, from 0 to 20 seconds. The straight line in the output of the From Workspace block reflects the block's linear extrapolation of missing data points at the end of the simulation.

Detection of Zero Crossings

If the input array contains more than one entry for the same time step, Simulink software detects a zero crossing at that time step. For example, suppose the input array has this data:

time:     0 1 2 2 3
signal:   2 3 4 5 6

At time 2, there is a zero crossing from input signal discontinuity. The effect of this zero crossing depends on the value of the Enable zero-crossing detection parameter. See Zero-Crossing Detection for more information.

Data Type Support

The From Workspace block accepts from the workspace and outputs real or complex signals of any type supported by Simulink software, including fixed-point and enumerated data types. Real signals of type double can be in either structure or matrix format. Complex signals and real signals of any type other than double must be in structure format.

Limitation: You cannot use a From Workspace block to import fixed-point data that is contained in a structure. Consider using a Simulink.Timeseries object instead of a structure.

Parameters and Dialog Box

Data: An expression that evaluates to an array or a structure containing an array of simulation times and corresponding signal values. For example, suppose that the workspace contains a column vector of times named T and a column vector of corresponding signal values named U. Entering the expression [T U] for this parameter yields the required input array. If the required signal-versus-time array or structure already exists in the workspace, enter the name of the structure or matrix in this field.
Sample time: Sample rate of data from the workspace. See How to Specify the Sample Time in the online documentation for more information.
Interpolate data: This option causes the block to linearly interpolate at time steps for which no corresponding workspace data exists. Otherwise, the current output equals the output at the most recent time for which data exists.
Enable zero-crossing detection: Select to enable zero-crossing detection. For more information, see Zero-Crossing Detection.
Form output after final data value by: Select method for generating output after the last time point for which data is available from the workspace.

Characteristics

Sample Time	Specified in the Sample time parameter
Scalar Expansion	No
Dimensionalized	Yes
Multidimensionalized	Yes
Zero-Crossing Detection	Yes, if enabled.

From Workspace - Read data from workspace

Library

Description

Using Data Saved by a To File Block

Using Data Saved by a To Workspace Block

Interpolating Missing Data Values

Interpolating Integer Data

Interpolating Boolean Data

Specifying Output After Final Data

Detection of Zero Crossings

Data Type Support

Parameters and Dialog Box

Characteristics

See Also

Related Products & Applications