oncentral Chi-squared PDF
y = distfun_ncx2pdf(x,k,delta)
a matrix of doubles, the outcome, greater or equal to zero
a matrix of doubles, the number of degrees of freedom, k>0 (can be non integer)
a matrix of doubles, the noncentrality parameter, delta>=0
a matrix of doubles, the probability density.
Computes the probability distribution function of the Noncentral Chi-squared distribution function.
Any scalar input argument is expanded to a matrix of doubles of the same size as the other input arguments.
Caution This distribution is known to have inferior accuracy in some cases.
The function definition is:
where is the chi-squared
probability density function with k+2i degrees of
freedom.
// Test with x scalar, k scalar computed = distfun_ncx2pdf(9,5,4) expected = 0.0756164 // Plot the function h=scf(); k = [2 2 2 4 4 4]; delta = [1 2 3 1 2 3]; cols = [1 2 3 4 5 6]; lgd = []; for i = 1:size(k,"c") x = linspace(0,10,1000); y = distfun_ncx2pdf ( x , k(i), delta(i)); plot(x,y) str = msprintf("k=%s, delta=%s",.. string(k(i)),string(delta(i))); lgd($+1) = str; end for i = 1:size(k,"c") hcc = h.children.children; hcc.children(size(k,"c") - i + 1).foreground = cols(i); end xtitle("Noncentral Chi-squared PDF","x","y") legend(lgd); | ![]() | ![]() |
http://en.wikipedia.org/wiki/Chi-squared_distribution