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ADE L Calculation: Numerical (?) issues

itos

I needed to rub my eyes multiple times to believe that. I have these two expressions in my ADE L:

dB10(mag(8*c1_dc/c3_dc/6)) + 10
dB10(mag(8/6*c1_dc/c3_dc)) + 10

Clearly they are EQUIVALENT. Just different order. The first produces 24.8607, the second one 23.6113 dB. That's nearly 1dB difference!!

c1_dc and c3_dc are nonlinearity coefficients which are extracted from a swept DC analysis. Their values are 100.916m and -4.39371m respectively. According to math, the first one is correct.

How can that be?

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  • Andrew Beckett

    It's not crazy. I was about to explain that this is because you have integer division. This can be rather useful, but you have to be aware that SKILL works this way (as do many, many other languages). So the 8/6 (left to right) ends up being 1, because both operands are integer. As soon as either operand is a float, the division is a floating point division rather than integer division. So make it 8.0/6 and all will be well with the world.

    I don't know what you mean about ADE replacing 8.0 with 0 in the expression editor. As far as I know, that does not happen. If it does, you'll have to give more details as to precisely what you're doing that makes this happen.

    Regards,

    Andrew.

Reply
  • Andrew Beckett

    It's not crazy. I was about to explain that this is because you have integer division. This can be rather useful, but you have to be aware that SKILL works this way (as do many, many other languages). So the 8/6 (left to right) ends up being 1, because both operands are integer. As soon as either operand is a float, the division is a floating point division rather than integer division. So make it 8.0/6 and all will be well with the world.

    I don't know what you mean about ADE replacing 8.0 with 0 in the expression editor. As far as I know, that does not happen. If it does, you'll have to give more details as to precisely what you're doing that makes this happen.

    Regards,

    Andrew.

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