Version:

Last Modified: January 12, 2018

Computes the cross correlation of two signals.

The correlation method to use.

This input is available only if both
**x**
and
**y**
are arrays or waveforms.

If
**x**
and
**y**
are small, the direct method typically is faster. If
**x**
and
**y**
are large, the frequency domain method typically is faster. Additionally, slight numerical differences can exist between the two methods.

Name | Description |
---|---|

direct |
Computes the cross correlation using the direct method of linear correlation. |

frequency domain |
Computes the cross correlation using an FFT-based technique. |

**Default:
**frequency domain

The normalization method to use to compute the cross correlation between the two input signals.

This input is available only if both
**x**
and
**y**
are arrays or waveforms.

Name | Description |
---|---|

none |
Does not apply normalization. |

unbiased |
Applies unbiased normalization. |

biased |
Applies biased normalization. |

**Default:
**none

Length of each set of x-values. This node computes each set of values separately.

**sample length x**
must be greater than 0.

This input is available only if
**x**
is a double-precision, floating-point number.

**Default:
**100

Length of each set of y-values. This node computes each set of values separately.

**sample length y**
must be greater than 0.

This input is available only if
**y**
is a double-precision, floating-point number.

**Default:
**100

Error conditions that occur before this node runs.

The node responds to this input according to standard error behavior.

Standard Error Behavior

Many nodes provide an
**error in**
input and an
**error out**
output so that the node can respond to and communicate errors that occur while code is running. The value of
**error in**
specifies whether an error occurred before the node runs. Most nodes respond to values of
**error in**
in a standard, predictable way.

**Default:
**No error

A Boolean that specifies whether to use the data points before the current block to compute the cross-correlation.

True | Uses the data points before the current block to compute the cross-correlation. |

False | Does not use the data points before the current block to compute the cross-correlation. |

This input is available only if one of the input sequences is a double-precision, floating-point number.

**Default:
**True

Error information.

The node produces this output according to standard error behavior.

Standard Error Behavior

**error in**
input and an
**error out**
output so that the node can respond to and communicate errors that occur while code is running. The value of
**error in**
specifies whether an error occurred before the node runs. Most nodes respond to values of
**error in**
in a standard, predictable way.

The cross correlation Rxy(*t*) of the sequences
*x*(*t*) and
*y*(*t*) is defined by the following equation:

$Rxy(t)=x(t)\otimes y(t)={\int}_{-\infty}^{\infty}x*(\tau )\cdot y(t+\tau )d\tau $

where the symbol $\otimes $ denotes correlation.

The discrete implementation of cross correlation is as follows. Let
${x}_{j}=0,\text{}j<0\text{}\text{}orj\ge N$

and

${y}_{j}=0,\text{}j<0\text{}\text{}or\text{}j\ge M$

Then this node obtains the elements of
*h*
using the following equation:

${h}_{j}=\sum _{k=0}^{N-1}{{x}_{k}}^{*}\cdot {y}_{j+k}$

for $j=-(N-1),-(N-2),\text{}\mathrm{...}\text{},-1,0,1,\text{}\mathrm{...}\text{},(M-2),(M-1)$

The elements of the output sequence
**Rxy**
are related to the elements in the sequence
*h*
by

${Rxy}_{i}={h}_{i-(N-1)}$

for $i=0,1,2,\mathrm{...}\text{},N+M-2$

Because you cannot index arrays with negative numbers, the corresponding cross correlation value at
*t*
= 0 is the
*N*
^{th}
element of the output sequence
**Rxy**. Therefore,
**Rxy**
represents the correlation values that this node shifts
*N*
times in indexing.

This node applies unbiased normalization as follows:

${R}_{xy}{\left(unbiased\right)}_{j}=\frac{1}{f\left(j\right)}{Rxy}_{j}$

for
*j*
= 0, 1, 2, ...,
*M*
+
*N*
- 2

where
*R*
_{xy}
is the cross correlation between
*x*
and
*y*
with no normalization.
*f*(*j*) is:

This node applies biased normalization as follows:

${R}_{xy}{\left(biased\right)}_{j}=\frac{1}{\mathrm{max}(M,N)}{Rxy}_{j}$

for
*j*
= 0, 1, 2, ...,
*M*
+
*N*
- 2

where
*R*
_{xy}
is the cross correlation between
*x*
and
*y*
with no normalization.

**Where This Node Can Run:
**

Desktop OS: Windows

FPGA: DAQExpress does not support FPGA devices

Web Server: Not supported in VIs that run in a web application