Commit e9dca5b6 authored by thomas.forbriger's avatar thomas.forbriger

[WP] (issue7): describe tow potential problems

parent eb09c535
......@@ -25,11 +25,24 @@ multiplication of the samples with the mpc factors. For this reason for any
exponent (except exponent being exactly zero) a division by zero takes place
for zero-offset traces.
The exepction might by just by chance. How is zero to the power of zero
The exception might by just by chance. How is zero to the power of zero
defined?
From the man page of the pow-function:
- The pow() function returns the value of x raised to the power of y.
- If y is 0, the result is 1.0 (even if x is a NaN).
We potentially face two problems:
- When using the zero offset (least offset) trace as a reference for offset
dependent scaling (as is the default), a division by zero happens in
subroutine mpcfactors.
- Zero offset traces may come with an mpc-scaling factor equal to zero. This
means, the trace should be down-scaled to a straight line in any case.
The current concept of trace scaling does this by leaving the sample values
of the trace as they are, by using a viewport for the trace according to
current clipping (derived in function settracevp) and by setting the world
coordinates for the trace's viewport appropriately (i.e. to infinity). In
the latter step there happens the nasty division by zero (division by mpc
factor). This problem is present, even is the zero offset trace is not used
as a reference.
----- END OF issue7_refract_catch_zero_offset.txt -----
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