Compute elementtoelement difference along specified dimension of input
Math Functions / Math Operations
dspmathops
The Difference block computes the difference between adjacent elements in rows, columns,
or a specified dimension of the input array u
. You can configure the block
to compute the difference only within the current input, or across consecutive inputs (running
difference).
When you set the Running difference parameter to
No
, the block computes the difference between adjacent elements
in the specified dimension of the current input. In this mode, the block can compute the
difference along the columns, rows, or a specified dimension of the input.
When you set the Difference along parameter to
Columns
, the block computes differences between adjacent
elements in each column of the input.
y = diff(u) % Equivalent MATLAB code
For MbyN inputs, the output is an (M – 1)byN matrix whose jth column has the following elements:
$${y}_{i,j}={u}_{i}{}_{+1}{,}_{j}{u}_{i,j}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}1\le i\le (M1)$$
When you set the Difference along parameter to
Rows
, the block computes differences between adjacent
elements in each row of the input.
y = diff(u,[],2) % Equivalent MATLAB code
The output is an Mby(N1) matrix whose ith row has the following elements:
$${y}_{i,j}={u}_{i,j+1}{u}_{i,j}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}1\le j\le (N1)$$
When you set the Difference along parameter to
Specified dimension
, the behavior of the block is an
extension of the rowwise differencing described earlier. The block computes differences
between adjacent elements along the dimension you specify in the
Dimension parameter.
y = diff(u,[],d) % Equivalent MATLAB code where d is the dimension
The output is an array whose length in the specified dimension is one less than that
of the input, and whose lengths in other dimensions are unchanged. For example, consider
an
MbyNbyPbyR
input array with elements u(i,j,k,l) and assume that
Dimension is 3
. The output of the block is an
MbyNby(P–1)byR
array with the following elements:
$${y}_{i,j,k,l}={u}_{i,j,k+1,l}{u}_{i,j,k,l}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}1\le k\le (P1)$$
When you set the Running difference parameter to
Yes
, the block computes the running difference along the
columns of the input.
For an MbyN input matrix, the output is an MbyN matrix whose jth column has the following elements:
$${y}_{i,j}={u}_{i+1,j}{u}_{i,j}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}2\le i\le (M1)$$
In running mode, the first element of the output for each column is the first input element minus the last input element of the previous frame. For the first frame, the block subtracts zero from the first input element.
$${y}_{1,j}(t)={u}_{1,j}(t){u}_{M,j}(t{T}_{f})$$
The following diagram shows the data types used within the Difference block for fixedpoint signals.
You can set the accumulator and output data types in the block dialog as discussed in Parameters .
For an example showing the modes of the Difference block, open ex_difference.
The following figure shows the output of the block when it is differencing along columns in nonrunning mode.
The following figure shows the output of the block when it is differencing along rows in nonrunning mode.
The following figure shows the second frame of block output when the block is computing the running difference.
Main Tab
Specify whether or not the block computes a running difference. When you select
No
, the block computes the difference between adjacent
elements in the current input. When you select Yes
, the block
computes the running difference across consecutive inputs. In running mode, the block
always computes the difference along the columns of the input. See Running Operation for more information.
Specify whether the block computes the difference along the columns, rows, or specified dimension of the input.
Specify the onebased dimension along which to compute elementtoelement differences.
This parameter is only visible when you select Specified
dimension
for the Difference along
parameter.
Data Types Tab
Floatingpoint inheritance takes precedence over the data type settings defined on this pane. When inputs are floating point, the block ignores these settings, and all internal data types are floating point.
Specify the rounding mode for fixedpoint operations as one of the following:
Floor
Ceiling
Convergent
Nearest
Round
Simplest
Zero
For more details, see rounding mode.
When you select this parameter, the block saturates the result of its fixedpoint
operation. When you clear this parameter, the block wraps the result of its fixedpoint
operation. For details on saturate
and wrap
, see
overflow mode for fixedpoint operations.
Specify the accumulator data type. See FixedPoint 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: Inherit via
internal rule
. For more information on this rule, see Inherit via Internal Rule.
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 Accumulator parameter.
See Specify Data Types Using Data Type Assistant (Simulink) for more information.
Specify the output data type. See FixedPoint Data Types for illustrations depicting the use of the output data type in this block. You can set it to:
A rule that inherits a data type, for example, Inherit: Same as
accumulator
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 Output parameter.
See Control Signal Data Types (Simulink) for more information.
Specify the minimum value that the block should output. The default value is
[]
(unspecified). Simulink^{®} uses this value to perform:
Simulation range checking (see Signal Ranges (Simulink))
Automatic scaling of fixedpoint data types
Specify the maximum value that the block should output. The default value is
[]
(unspecified). Simulink uses this value to perform:
Simulation range checking (see Signal Ranges (Simulink))
Automatic scaling of fixedpoint data types
Select this parameter to prevent the fixedpoint tools from overriding the data types you specify on the block mask.
Port  Supported Data Types 

Input 

Output 
