I need to evaluate...
IF(t,1,0) (If t is true, output 1, if t is false, output 0 (numeric), t may be something like V11 >= 7, for example)
BUT I have no IF statement handling capability at this level of a simulation.
I do have algebraic capability.
Is there some cute way to do this algebraically?
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et |
X=int(V11/7) X/X
gah! messed that up :S
For your example, V11>=3D7:
(abs(V11-7))/(V11-7) will be +1 for V11>7, -1 for V11
t=X/X
This will sorta work, but if x is 0 then you'll probably get errors, to a human it's the 0/0 = 1 thing not having used your emulator I can't be sure what'll happen of how to treat an error like this.
I don't have INT available, I do have ABS and some trig functions
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et |
That's what I came up with, except I inserted a small "delta" (smaller than my step size) to avoid 0/0. I was hoping for something more compact :-(
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et |
Do you have a unit step function (u(x)) available?
-- Paul Hovnanian paul@hovnanian.com ----------------------------------------------------------------------
No :-(
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et |
I don't have function SGN :-(
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et |
(1+sgn(V11-7))/2 ?
y = V11 -7
(abs(y) + y)/(2*y)
P.S. If you want avoid awkward situations very near y == 0 you could do
(abs(y) + y)/(2* abs(y) + e)
where e is a very small positive number
are there any operators or functions that can give a different mumeric result depending on the truth of the input.
many systems have false as 0 and true as 1 (or less common -1)
else maybe something like (sgn( sgn(V11-7) *2 +1 ) + 1 ) /2
ABS has an intrinsic "if" that can do it. Spehro showed the method.
(numeric),
Do you have a tanh() function?
No, Though I'm fascinated. How would use of TANH() work in this situation?
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et |
tanh(x) = (e^x - e^-x) / (e^x + e^-x), so for large |x| (for example, |x| > 3) it approximates x/abs(x) quite closely but avoids divide-by-zero issues. For snappier results, consider tanh(k*x), at the risk of overflow if k is too big.
.-- jiw
So the equivalent of "SGN"?
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et |
(numeric),
With tanh(Ax-B)/2 + 1/2 you may arbitrarily make close approximation to a unit step function (including shiftability). Or do interesting cross fade like things. Mostly pretty well behaved for numerical techniques as well.
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