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Overflows and underflows are logged as warnings for all assignment, plus, minus, and multiplication operations when the fipref LoggingMode property is set to on. For example, try the following:
a = fi(1:5,1,8,6);
F = a.fimath; F.SumMode = 'SpecifyPrecision'; F.ProductMode = 'SpecifyPrecision'; a.fimath = F;
P = fipref; P.LoggingMode = 'on';
P.NumericTypeDisplay = 'none'; P.FimathDisplay = 'none';
a.SumWordLength = 16; a.SumFractionLength = 15; a.ProductWordLength = 16; a.ProductFractionLength = 15;
a(1) = pi Warning: 1 overflow occurred in the fi assignment operation. a = 1.9844 1.9844 1.9844 1.9844 1.9844 a(1) = double(eps(a))/10 Warning: 1 underflow occurred in the fi assignment operation. a = 0 1.9844 1.9844 1.9844 1.9844
a+a Warning: 12 overflows occurred in the fi + operation. ans = 0 1.0000 1.0000 1.0000 1.0000 a-a Warning: 8 overflows occurred in the fi - operation. ans = 0 0 0 0 0
a.*a Warning: 4 product overflows occurred in the fi .* operation. ans = 0 1.0000 1.0000 1.0000 1.0000 a*a' Warning: 4 product overflows occurred in the fi * operation. Warning: 3 sum overflows occurred in the fi * operation. ans = 1.0000
The final example above is a complex multiplication that requires both multiplication and addition operations. The warnings inform you of overflows and underflows in both.
Because overflows and underflows are logged as warnings, you can use the dbstop MATLAB® function with the syntax
dbstop if warning
to find the exact lines in a file that are causing overflows or underflows.
dbstop if warning fi:underflow
to stop only on lines that cause an underflow. Use
dbstop if warning fi:overflow
to stop only on lines that cause an overflow.
When the fipref LoggingMode property is set to on, you can use the following functions to return logged information about assignment and creation operations to the MATLAB command line:
maxlog — Returns the maximum real-world value
minlog — Returns the minimum value
noverflows — Returns the number of overflows
nunderflows — Returns the number of underflows
LoggingMode must be set to on before you perform any operation in order to log information about it. To clear the log, use the function resetlog.
For example, consider the following. First turn logging on, then perform operations, and then finally get information about the operations:
fipref('LoggingMode','on'); x = fi([-1.5 eps 0.5], true, 16, 15); x(1) = 3.0; maxlog(x) ans = 1.0000 minlog(x) ans = -1 noverflows(x) ans = 2 nunderflows(x) ans = 1
Next, reset the log and request the same information again. Note that the functions return empty , because logging has been reset since the operations were run:
resetlog(x) maxlog(x) ans =  minlog(x) ans =  noverflows(x) ans =  nunderflows(x) ans =