Subtract Function

Computes the difference of the inputs.

If you wire two waveform values or two dynamic data type values to this function, error in and error out terminals appear on the function. Subtracting two time stamp values yields a numeric value (difference in time), and subtracting a numeric value from a time stamp value yields a time stamp. You cannot subtract a time stamp value from a numeric value. The dimensions of two matrices that you want to subtract must be the same. Otherwise, this function returns an empty matrix. The connector pane displays the default data types for this polymorphic function.


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Inputs/Outputs

  • cdbl.png x —

    x specifies the input value.

    This input accepts the following data types:
    • Number
    • Timestamp
    • Analog Waveform
    This input also accepts an array or an array of clusters of the listed data types.
  • cdbl.png y —

    y can be a scalar number, a fixed-point number, an array or cluster of numbers, an array of clusters of numbers, a time stamp, and so on.

  • idbl.png x-y —

    x-y is the difference between x and y.

    Note You can manually configure this function to output data of a type you want. To specify the output data type, right-click the function and select Properties to display the Object Properties dialog box. On the Output Configuration page, click the Representation icon and select the data type you want. A blue coercion dot appears on the output terminal of the function to indicate that you have configured the output data type.

    • When you wire matrix data as an input to this function, a VI that includes subVIs that work with the matrix data type replaces the function. The resulting VI has the same icon but contains a matrix-specific algorithm. The node remains a VI if you disconnect the matrix from the input(s). Wire other data types as inputs to restore the original function. If you wire a data type to a function and that data type causes a basic math operation to fail, the function returns an empty matrix or NaN.

    Fixed-Point Details

    If you wire fixed-point values to Numeric functions such as Add, Subtract, Multiply, and Square, the functions usually return values that do not lose any bits of word length. However, if the operation creates a value that exceeds the maximum word length that LabVIEW accepts, overflow or rounding conditions can occur. LabVIEW accepts a maximum word length of 64 bits. Use the Numeric Node Properties dialog box to configure how LabVIEW handles overflow or rounding of fixed-point data.

    FPGA Module Details

    The following details apply when you use this object in an FPGA VI.

    Note The following details are subject to change with each version of the LabVIEW FPGA Module.
    Single-Cycle Timed Loop Supported.
    Usage If you use this function with the single-precision floating-point data type, refer to the Using the Single-Precision Floating-Point Data Type and Deciding Which Data Type to Use in FPGA Designs topics for resource use, latency, and single-cycle Timed Loop support implications.
    Timing

    Inside single-cycle Timed Loop--When you use this function inside a single-cycle Timed Loop, the combinatorial logic delay is proportional to the number of bits in x or y, whichever data type is larger.

    Outside single-cycle Timed Loop--When you use this function outside a single-cycle Timed Loop, it takes one clock cycle and uses one register.

    If you use this function with the fixed-point data type, the overflow and rounding modes might impact timing.

    Resources This function requires FPGA resources proportional to the number of bits in x or y, whichever data type is larger. If you use this function with the fixed-point data type, the overflow and rounding modes might impact resources.

    Examples

    Refer to the following example files included with LabVIEW.

    • labview\examples\Numerics\Numeric Functions.vi