The following is in the Release Notes for R2009b. However, explicitly turning on the warning does not enable it for me, in R2011a. I don't see the warning on the screen, or using the lastwarn() function.
Divide By Zero and Log Of Zero Warnings Off By Default
MATLAB no longer displays Divide by zero and Log of zero warnings unless you explicitly enable them with the following commands:
warning on MATLAB:divideByZero
warning on MATLAB:log:LogOfZero
This only affects the display of the warning message on the screen; the warning status is still updated as usual.
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