Is there a bug in the IFIR function in the Filter Design Toolbox 2.5 (R13+)?

The IFIR does not converge for any ripple value greater than 0.004.

For example:

[h,g] = ifir(4,'low',[.05 .08], [0.01 0.005]);

returns the following error:

 *** FAILURE TO CONVERGE ***

 Probable cause is machine rounding error.

 Number of iterations = 3 Warning:

 If the number of iterations exceeds 3, the design may

 be correct, but should be verified with freqz.

Answer 1

[MathWorks Support Team]

This bug has been fixed for Release 14 (R14). For previous releases, read below for any possible workarounds:

This is a bug in the Filter Design Toolbox 2.5 (R13) when using ripple value greater than 0.004 with the IFIR function.

To work around this issue, use the 'advanced' option with the IFIR function. For example:

[h,g] = ifir(4,'low',[.05 .08], [0.01 0.01],'adv');