# NAG CL Interfaceg03bdc (rot_​promax)

## 1Purpose

g03bdc calculates a ProMax rotation, given information following an orthogonal rotation.

## 2Specification

 #include
 void g03bdc (Nag_RotationLoading stand, Integer n, Integer m, const double x[], Integer pdx, const double ro[], Integer pdro, double power, double fp[], Integer pdfp, double r[], Integer pdr, double phi[], Integer pdphi, double fs[], Integer pdfs, NagError *fail)
The function may be called by the names: g03bdc, nag_mv_rot_promax or nag_mv_promax.

## 3Description

Let $X$ and $Y$ denote $n$ by $m$ matrices each representing a set of $n$ points in an $m$-dimensional space. The $X$ matrix is a matrix of loadings as returned by g03bac, that is following an orthogonal rotation of a loadings matrix $Z$. The target matrix $Y$ is calculated as a power transformation of $X$ that preserves the sign of the loadings. Let ${X}_{ij}$ and ${Y}_{ij}$ denote the $\left(i,j\right)$th element of matrices $X$ and $Y$. Given a value greater than $1$ for the exponent $p$:
 $Yij = δij Xij p ,$
for
• $i=1,2,\dots ,n$;
• $j=1,2,\dots ,m$;
• ${\delta }_{ij}=\left\{\begin{array}{c}-1\text{, if ​}{X}_{ij}<0\text{; ​}\\ 1\text{, otherwise.}\end{array}\right\$
The above power transformation tends to increase the difference between high and low values of loadings and is intended to increase the interpretability of a solution.
In the second step a solution of:
 $XW=Y , X,Y ∈ ℝn×m , ​ W ∈ ℝm×m ,$
is found for $W$ in the least squares sense by use of singular value decomposition of the orthogonal loadings $X$. The ProMax rotation matrix $R$ is then given by
 $R=OW W~ , O, ​ W~ ∈ ℝm×m ,$
where $O$ is the rotation matrix from an orthogonal transformation, and $\stackrel{~}{W}$ is a matrix with the square root of diagonal elements of ${\left({W}^{\mathrm{T}}W\right)}^{-1}$ on its diagonal and zeros elsewhere.
The ProMax factor pattern matrix $P$ is given by
 $P = X W W~ , P ∈ ℝn×m ;$
the inter-factor correlations $\Phi$ are given by
 $Φ= QT Q-1 , Φ ∈ ℝm×m ;$
where $Q=W\stackrel{~}{W}$; and the factor structure $S$ is given by
 $S=PΦ , S ∈ ℝn×m .$
Optionally, the rows of target matrix $Y$ can be scaled by the communalities of loadings.

None.

## 5Arguments

1: $\mathbf{stand}$Nag_RotationLoading Input
${\mathbf{stand}}=\mathrm{Nag_RoLoadStand}$
Rows of $Y$ are (Kaiser) normalized by the communalities of the loadings.
${\mathbf{stand}}=\mathrm{Nag_RoLoadNotStand}$
Rows are not normalized.
Constraint: ${\mathbf{stand}}=\mathrm{Nag_RoLoadNotStand}$ or $\mathrm{Nag_RoLoadStand}$.
2: $\mathbf{n}$Integer Input
On entry: $n$, the number of points.
Constraint: ${\mathbf{n}}\ge {\mathbf{m}}$.
3: $\mathbf{m}$Integer Input
On entry: $m$, the number of dimensions.
Constraint: ${\mathbf{m}}\ge 1$.
4: $\mathbf{x}\left[{\mathbf{n}}×{\mathbf{pdx}}\right]$const double Input
Note: the $\left(i,j\right)$th element of the matrix $X$ is stored in ${\mathbf{x}}\left[\left(i-1\right)×{\mathbf{pdx}}+j-1\right]$.
On entry: the loadings matrix following an orthogonal rotation, $X$.
5: $\mathbf{pdx}$Integer Input
On entry: the stride separating matrix column elements in the array x.
Constraint: ${\mathbf{pdx}}\ge {\mathbf{m}}$.
6: $\mathbf{ro}\left[{\mathbf{m}}×{\mathbf{pdro}}\right]$const double Input
Note: the $\left(i,j\right)$th element of the matrix is stored in ${\mathbf{ro}}\left[\left(i-1\right)×{\mathbf{pdro}}+j-1\right]$.
On entry: the orthogonal rotation matrix, $O$.
7: $\mathbf{pdro}$Integer Input
On entry: the stride separating matrix column elements in the array ro.
Constraint: ${\mathbf{pdro}}\ge {\mathbf{m}}$.
8: $\mathbf{power}$double Input
On entry: $p$, the value of exponent.
Constraint: ${\mathbf{power}}>1.0$.
9: $\mathbf{fp}\left[{\mathbf{n}}×{\mathbf{pdfp}}\right]$double Output
Note: the $\left(i,j\right)$th element of the matrix is stored in ${\mathbf{fp}}\left[\left(i-1\right)×{\mathbf{pdfp}}+j-1\right]$.
On exit: the factor pattern matrix, $P$.
10: $\mathbf{pdfp}$Integer Input
On entry: the stride separating matrix column elements in the array fp.
Constraint: ${\mathbf{pdfp}}\ge {\mathbf{m}}$.
11: $\mathbf{r}\left[{\mathbf{m}}×{\mathbf{pdr}}\right]$double Output
Note: the $\left(i,j\right)$th element of the matrix $R$ is stored in ${\mathbf{r}}\left[\left(i-1\right)×{\mathbf{pdr}}+j-1\right]$.
On exit: the ProMax rotation matrix, $R$.
12: $\mathbf{pdr}$Integer Input
On entry: the stride separating matrix column elements in the array r.
Constraint: ${\mathbf{pdr}}\ge {\mathbf{m}}$.
13: $\mathbf{phi}\left[{\mathbf{m}}×{\mathbf{pdphi}}\right]$double Output
Note: the $\left(i,j\right)$th element of the matrix is stored in ${\mathbf{phi}}\left[\left(i-1\right)×{\mathbf{pdphi}}+j-1\right]$.
On exit: the matrix of inter-factor correlations, $\Phi$.
14: $\mathbf{pdphi}$Integer Input
On entry: the stride separating matrix column elements in the array phi.
Constraint: ${\mathbf{pdphi}}\ge {\mathbf{m}}$.
15: $\mathbf{fs}\left[{\mathbf{n}}×{\mathbf{pdfs}}\right]$double Output
Note: the $\left(i,j\right)$th element of the matrix is stored in ${\mathbf{fs}}\left[\left(i-1\right)×{\mathbf{pdfs}}+j-1\right]$.
On exit: the factor structure matrix, $S$.
16: $\mathbf{pdfs}$Integer Input
On entry: the stride separating matrix column elements in the array fs.
Constraint: ${\mathbf{pdfs}}\ge {\mathbf{m}}$.
17: $\mathbf{fail}$NagError * Input/Output
The NAG error argument (see Section 7 in the Introduction to the NAG Library CL Interface).

## 6Error Indicators and Warnings

NE_ALLOC_FAIL
Dynamic memory allocation failed.
NE_INT
On entry, ${\mathbf{m}}=〈\mathit{\text{value}}〉$.
Constraint: ${\mathbf{m}}\ge 1$.
On entry, ${\mathbf{pdfp}}=〈\mathit{\text{value}}〉$.
Constraint: ${\mathbf{pdfp}}>0$.
On entry, ${\mathbf{pdfs}}=〈\mathit{\text{value}}〉$.
Constraint: ${\mathbf{pdfs}}>0$.
On entry, ${\mathbf{pdphi}}=〈\mathit{\text{value}}〉$.
Constraint: ${\mathbf{pdphi}}>0$.
On entry, ${\mathbf{pdr}}=〈\mathit{\text{value}}〉$.
Constraint: ${\mathbf{pdr}}>0$.
On entry, ${\mathbf{pdro}}=〈\mathit{\text{value}}〉$.
Constraint: ${\mathbf{pdro}}>0$.
On entry, ${\mathbf{pdx}}=〈\mathit{\text{value}}〉$.
Constraint: ${\mathbf{pdx}}>0$.
NE_INT_2
On entry, ${\mathbf{n}}=〈\mathit{\text{value}}〉$ and ${\mathbf{m}}=〈\mathit{\text{value}}〉$.
Constraint: ${\mathbf{n}}\ge {\mathbf{m}}$.
On entry, ${\mathbf{pdfp}}=〈\mathit{\text{value}}〉$ and ${\mathbf{m}}=〈\mathit{\text{value}}〉$.
Constraint: ${\mathbf{pdfp}}\ge {\mathbf{m}}$.
On entry, ${\mathbf{pdfs}}=〈\mathit{\text{value}}〉$ and ${\mathbf{m}}=〈\mathit{\text{value}}〉$.
Constraint: ${\mathbf{pdfs}}\ge {\mathbf{m}}$.
On entry, ${\mathbf{pdphi}}=〈\mathit{\text{value}}〉$ and ${\mathbf{m}}=〈\mathit{\text{value}}〉$.
Constraint: ${\mathbf{pdphi}}\ge {\mathbf{m}}$.
On entry, ${\mathbf{pdr}}=〈\mathit{\text{value}}〉$ and ${\mathbf{m}}=〈\mathit{\text{value}}〉$.
Constraint: ${\mathbf{pdr}}\ge {\mathbf{m}}$.
On entry, ${\mathbf{pdro}}=〈\mathit{\text{value}}〉$ and ${\mathbf{m}}=〈\mathit{\text{value}}〉$.
Constraint: ${\mathbf{pdro}}\ge {\mathbf{m}}$.
On entry, ${\mathbf{pdx}}=〈\mathit{\text{value}}〉$ and ${\mathbf{m}}=〈\mathit{\text{value}}〉$.
Constraint: ${\mathbf{pdx}}\ge {\mathbf{m}}$.
NE_INTERNAL_ERROR
An internal error has occurred in this function. Check the function call and any array sizes. If the call is correct then please contact NAG for assistance.
NE_REAL_ARG_LE
On entry, ${\mathbf{power}}=〈\mathit{\text{value}}〉$.
Constraint: ${\mathbf{power}}>1.0$.
NE_SVD_FAIL
SVD failed to converge.

## 7Accuracy

The calculations are believed to be stable.

## 8Parallelism and Performance

g03bdc is threaded by NAG for parallel execution in multithreaded implementations of the NAG Library.
g03bdc makes calls to BLAS and/or LAPACK routines, which may be threaded within the vendor library used by this implementation. Consult the documentation for the vendor library for further information.
Please consult the X06 Chapter Introduction for information on how to control and interrogate the OpenMP environment used within this function. Please also consult the Users' Note for your implementation for any additional implementation-specific information.

None.

## 10Example

This example reads a loadings matrix and calculates a varimax transformation before calculating $P$, $R$ and $\sigma$ for a ProMax rotation.

### 10.1Program Text

Program Text (g03bdce.c)

### 10.2Program Data

Program Data (g03bdce.d)

### 10.3Program Results

Program Results (g03bdce.r)