Partial least-squares regression

`[XL,YL] = plsregress(X,Y,ncomp)`

[XL,YL,XS] = plsregress(X,Y,ncomp)

[XL,YL,XS,YS] = plsregress(X,Y,ncomp)

[XL,YL,XS,YS,BETA] = plsregress(X,Y,ncomp,...)

[XL,YL,XS,YS,BETA,PCTVAR] = plsregress(X,Y,ncomp)

[XL,YL,XS,YS,BETA,PCTVAR,MSE] = plsregress(X,Y,ncomp)

[XL,YL,XS,YS,BETA,PCTVAR,MSE] = plsregress(...,* param1*,

`val1`

`param2`

`val2`

[XL,YL,XS,YS,BETA,PCTVAR,MSE,stats] = plsregress(X,Y,ncomp,...)

`[XL,YL] = plsregress(X,Y,ncomp)`

computes
a partial least-squares (PLS) regression of `Y`

on `X`

,
using `ncomp`

PLS components, and returns the predictor
and response loadings in `XL`

and `YL`

,
respectively. `X`

is an *n*-by-*p* matrix
of predictor variables, with rows corresponding to observations and
columns to variables. `Y`

is an *n*-by-*m* response
matrix. `XL`

is a *p*-by-`ncomp`

matrix
of predictor loadings, where each row contains coefficients that define
a linear combination of PLS components that approximate the original
predictor variables. `YL`

is an *m*-by-`ncomp`

matrix
of response loadings, where each row contains coefficients that define
a linear combination of PLS components that approximate the original
response variables.

`[XL,YL,XS] = plsregress(X,Y,ncomp)`

returns
the predictor scores `XS`

, that is, the PLS components
that are linear combinations of the variables in `X`

. `XS`

is
an *n*-by-`ncomp`

orthonormal matrix
with rows corresponding to observations and columns to components.

`[XL,YL,XS,YS] = plsregress(X,Y,ncomp)`

returns the response scores `YS`

, that is, the linear
combinations of the responses with which the PLS components `XS`

have
maximum covariance. `YS`

is an *n*-by-`ncomp`

matrix
with rows corresponding to observations and columns to components. `YS`

is
neither orthogonal nor normalized.

`plsregress`

uses the SIMPLS algorithm, first
centering `X`

and `Y`

by subtracting
off column means to get centered variables `X0`

and `Y0`

.
However, it does not rescale the columns. To perform PLS with standardized
variables, use `zscore`

to normalize `X`

and `Y`

.

If `ncomp`

is omitted, its default value is `min(size(X,1)-1,size(X,2))`

.

The relationships between the scores, loadings, and centered
variables `X0`

and `Y0`

are:

`XL = (XS\X0)' = X0'*XS`

,

`YL = (XS\Y0)' = Y0'*XS`

,

`XL`

and `YL`

are the coefficients
from regressing `X0`

and `Y0`

on `XS`

,
and `XS*XL'`

and `XS*YL'`

are the
PLS approximations to `X0`

and `Y0`

.

`plsregress`

initially computes `YS`

as:

`YS = Y0*YL = Y0*Y0'*XS`

,

By convention, however, `plsregress`

then
orthogonalizes each column of `YS`

with respect to
preceding columns of `XS`

, so that `XS'*YS`

is
lower triangular.

`[XL,YL,XS,YS,BETA] = plsregress(X,Y,ncomp,...)`

returns the PLS regression
coefficients `BETA`

. `BETA`

is a
(*p*+1)-by-*m* matrix, containing intercept terms
in the first row:

`Y = [ones(n,1),X]*BETA + Yresiduals`

,

`Y0 = X0*BETA(2:end,:) + Yresiduals`

. Here `Yresiduals`

is
the vector of response residuals.

`[XL,YL,XS,YS,BETA,PCTVAR] = plsregress(X,Y,ncomp)`

returns
a 2-by-`ncomp`

matrix `PCTVAR`

containing
the percentage of variance explained by the model. The first row of `PCTVAR`

contains
the percentage of variance explained in `X`

by each
PLS component, and the second row contains the percentage of variance
explained in `Y`

.

`[XL,YL,XS,YS,BETA,PCTVAR,MSE] = plsregress(X,Y,ncomp)`

returns
a 2-by-(`ncomp`

+1) matrix `MSE`

containing
estimated mean-squared errors for PLS models with `0:ncomp`

components.
The first row of `MSE`

contains mean-squared errors
for the predictor variables in `X`

, and the second
row contains mean-squared errors for the response variable(s) in `Y`

.

`[XL,YL,XS,YS,BETA,PCTVAR,MSE] = plsregress(...,`

specifies
optional parameter name/value pairs from the following table to control
the calculation of * param1*,

`val1`

`param2`

`val2`

`MSE`

.Parameter | Value |
---|---|

`'cv'` | The method used to compute When the value is a positive integer `k` ,`plsregress` uses`k` -fold cross-validation.When the value is an object of the `cvpartition` class, other forms of cross-validation can be specified.When the value is `'resubstitution'` ,`plsregress` uses`X` and`Y` both to fit the model and to estimate the mean-squared errors, without cross-validation.
The default is |

`'mcreps'` | A positive integer indicating the number of Monte-Carlo
repetitions for cross-validation. The default value is |

`options` | A structure that specifies whether to run in parallel, and specifies the random stream
or streams. Create the `UseParallel` — Set to`true` to compute in parallel. Default is`false` .`UseSubstreams` — Set to`true` to compute in parallel in a reproducible fashion. Default is`false` . To compute reproducibly, set`Streams` to a type allowing substreams:`'mlfg6331_64'` or`'mrg32k3a'` .`Streams` — A`RandStream` object or cell array consisting of one such object. If you do not specify`Streams` ,`plsregress` uses the default stream.
To compute in parallel, you need Parallel Computing Toolbox™ |

`[XL,YL,XS,YS,BETA,PCTVAR,MSE,stats] = plsregress(X,Y,ncomp,...)`

returns a
structure `stats`

with the following fields:

`W`

— A*p*-by-`ncomp`

matrix of PLS weights so that`XS = X0*W`

.`T2`

— The*T*^{2}statistic for each point in`XS`

.`Xresiduals`

— The predictor residuals, that is,`X0-XS*XL'`

.`Yresiduals`

— The response residuals, that is,`Y0-XS*YL'`

.

[1] de Jong, S. “SIMPLS: An Alternative
Approach to Partial Least Squares Regression.” *Chemometrics
and Intelligent Laboratory Systems*. Vol. 18, 1993, pp.
251–263.

[2] Rosipal, R., and N. Kramer. “Overview
and Recent Advances in Partial Least Squares.” *Subspace,
Latent Structure and Feature Selection: Statistical and Optimization
Perspectives Workshop (SLSFS 2005), Revised Selected Papers (Lecture
Notes in Computer Science 3940)*. Berlin, Germany: Springer-Verlag,
2006, pp. 34–51.