## ChiSqrCumulative

##### >Psychtoolbox>PsychProbability

prob = ChiSqrCumulative(X2,v)

Computes the chi-squared probability function. ChiSqrCumulative(X2,v)

returns P(X2|v), the probability of observing a chi-squared value <= X2

with v degrees of freedom. This is the probability that the sum of

squares of v unit-variance normally-distributed random variables is <=

X2. X2 and v may be matrices of the same size size, or either may be a

scalar.

e.g., ChiSqrCumulative(5.99,2) returns 0.9500, verifying the 95%

confidence bound for 2 degrees of freedom. This is also cross-checked in,

e.g., Abramowitz & Stegun Table 26.8

References: Press et al., Numerical Recipes, Cambridge, 1986;

Abramowitz & Stegun, Handbook of Mathematical Functions, Dover, 1972.

Peter R. Shaw, Woods Hole Oceanographic Institution

Woods Hole, MA 02543

(508) 457-2000 ext. 2473 pshaw@aqua.whoi.edu

March, 1990

Computed using the Incomplete Gamma function, as given by

Press et al. (Recipes) eq. (6.2.17)

`Psychtoolbox/PsychProbability/ChiSqrCumulative.m`