x2fx (Statistics Toolbox)

x2fx	Examples See Also

Transform a factor settings matrix to a design matrix.

Syntax

D = x2fx(X)
D = x2fx(X,'model')

Description

D = x2fx(X) transforms a matrix of system inputs, X, to a design matrix for a linear additive model with a constant term.

D = x2fx(X,'model') allows control of the order of the regression model.'model' can be one of these strings:

'interaction' - includes constant, linear, and cross product terms.
'quadratic' - interactions plus squared terms.
'purequadratic' - includes constant, linear and squared terms.

Alternatively, the argument, model, can be a matrix of terms. In this case each row of model represents one term. The value in a column is the exponent to raise the same column in X for that term. This allows for models with polynomial terms of arbitrary order.

x2fx is a utility function for rstool, regstats and cordexch.

Example

x = [1 2 3;4 5 6]'; model = 'quadratic';
D = x2fx(x,model)

D =

     1     1     4     4     1    16
     1     2     5    10     4    25
     1     3     6    18     9    36

Let x₁be the first column of x and x₂ be the second. Then, the first column of D is for the constant term. The second column is x₁. The 3rd column is x₂. The 4th is x₁x₂. The fifth is x₁²and the last is x₂².