The ichi2cdf function calculates the inverse chi-squared cumulative distribution function (CDF).

Synopsis

ichi2cdf(p,k)

Summary

The inverse chi-squared CDF returns the inverse of the chi-squared CDF with degrees of freedom k for the corresponding probability p.

Example

To calculate the inverse chi-squared distribution for a system consisting of numbers 1–10 with degree of freedom 5, do the following:

Create a 1-dimensional array called system_array of size 10 and a double attribute called system, and fill it with values 1–10.
```
AFL% store(build(<system:double>[i=0:9], double(i+1)), system_array); 
```

Apply the direct chi2cdf to the system attribute and store the result in target_array:

AFL% store(apply(system_array, direct, chi2cdf(system, 5)), target_array);

The output is:

{i} system,direct
{0} 1,0.0374342
{1} 2,0.150855
{2} 3,0.300014
{3} 4,0.450584
{4} 5,0.58412
{5} 6,0.693781
{6} 7,0.77936
{7} 8,0.843764
{8} 9,0.890936
{9} 10,0.924765

Apply the ichi2cdf function to the attribute direct:

AFL% apply(target_array, inverse, ichi2cdf(direct, 5.0));

The output is:

{i} system,direct,inverse
{0} 1,0.0374342,1
{1} 2,0.150855,2
{2} 3,0.300014,3
{3} 4,0.450584,4
{4} 5,0.58412,5
{5} 6,0.693781,6
{6} 7,0.77936,7
{7} 8,0.843764,8
{8} 9,0.890936,9
{9} 10,0.924765,10

Note that the new attribute inverse is equal to the original system attribute.

Remove the example arrays:

AFL% remove(system_array); remove(target_array);

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