Floating-point addition is not associative or distributive. It looks
like you have some roundoff error that is greater than the comparison
tolerance but less than the print precision.
Henry Rich
On 1/9/2022 12:23 PM, Pawel Jakubas wrote:
Dear J users,
I am testing very simple multiplication property:
s (A+B) = sA + sB
using emulated property testing (more on this here
https://github.com/paweljakubas/j-random-matrices/blob/main/chapters/algebra.md#testing-matrix-properties
)
So basically I am doing something like this:
NB. picking a random scalar from (-100,100), and a random matrix having
elements from (-1000,1000) and y being shape
genUniformMatrix=: 3 : 'y $ _1000 1000 runiform ((0{y) * (1{y))'
runiform is defined here
https://github.com/paweljakubas/j-random-matrices/blob/main/j/algebra.ijs#L206
data=:(_100 100 runiform 1);((genUniformMatrix 50 50),:(genUniformMatrix 50
50))
NB. now I define relation I want to verify
leftR=: 4 : '(0{x) * ( (0{y) + (1{y) )'
rightR=: 4 : '( (0{x) * (0{y) ) + ( (0{x) * (1{y) )'
relation=: leftR`rightR
NB. finally I want to have a check of relation using relation and data
checkEqOfMatricesScalarsRel=: 4 : '( (>0{y) x@.0 (>1{y) ) -: ( (>0{y) x@.1
(>1{y) )'
NB. Everything good until now. then I start to check it
relation checkEqOfMatricesScalarsRel data
1
NB. then I regenerate random data and at some moment I got
relation checkEqOfMatricesScalarsRel data
0
NB. Which is what I did not expect of course, so I dig into it and I modify
checkEqOfMatricesScalarsRel=: 4 : '( (>0{y) x@.0 (>1{y) ) = ( (>0{y) x@.1
(>1{y) )'
((>0{data) relation@.0 (>1{data)) = ((>0{data) relation@.1 (>1{data))
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(<(<26),(<37)) { ( ((>0{data) relation@.0 (>1{data)) = ((>0{data)
relation@.1 (>1{data)) )
0
(<(<26),(<37)) { ( ((>0{data) relation@.0 (>1{data)) )
41.773
(<(<26),(<37)) { ( ((>0{data) relation@.1 (>1{data)) )
41.773
((<(<26),(<37)) { ( ((>0{data) relation@.0 (>1{data)) )) =
((<(<26),(<37)) { ( ((>0{data) relation@.1 (>1{data)) ))
0
And this is very strange, as I have the same number in both sides of
relation but they contribute to 0 upon comparison (and I expect 1 of
course).
Does anyone understand the nature of this inconsistency? Or give me a hint
what should be done to avoid things like that?
I use 902.
Thanks in advance,
Pawel Jakubas
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