Scaling in sigma inGaussian wrong

[roflmaostc]

julia> gaussian((10,1), sigma=1)
10×1 IndexFunArray{Float64, 2, IndexFunArrays.var"#g#290"{Float64, Tuple{Int64, Int64}, Tuple{Float64, Float64}, Int64}}:
 3.726653172078671e-6
 0.00033546262790251185
 0.011108996538242306
 0.1353352832366127
 0.6065306597126334
 1.0
 0.6065306597126334
 0.1353352832366127
 0.011108996538242306
 0.00033546262790251185

julia> gaussian((10,1), sigma=0.1, scale=0.1)
10×1 IndexFunArray{Float64, 2, IndexFunArrays.var"#g#290"{Float64, Tuple{Int64, Int64}, Tuple{Float64, Float64}, Int64}}:
 5.166420632838008e-55
 1.8048513878454407e-35
 2.862518580549414e-20
 2.0611536224385653e-9
 0.006737946999085473
 1.0
 0.006737946999085473
 2.0611536224385653e-9
 2.862518580549414e-20
 1.8048513878454407e-35

julia> gaussian((10,1), sigma=sqrt(0.1), scale=0.1)
10×1 IndexFunArray{Float64, 2, IndexFunArrays.var"#g#290"{Float64, Tuple{Int64, Int64}, Tuple{Float64, Float64}, Int64}}:
 3.726653172078671e-6
 0.00033546262790251185
 0.011108996538242306
 0.1353352832366127
 0.6065306597126334
 1.0
 0.6065306597126334
 0.1353352832366127
 0.011108996538242306
 0.00033546262790251185

[roflmaostc]

Offset still has the issue that it's not scaled properly.

So the offset is in pixel coordinates instead of scaled coordinates

[roflmaostc]

I'm not sure if this is easily fixable

IndexFunArrays.jl/src/scalar_ifas.jl

Line 20 in a8bdc58

x_expr8 = :(exp(.- sum(abs2.(x .- offset).*scale))) # scale is 1/(2 sigma^2)

[RainerHeintzmann]

Well.... offset is defined in pixels always like this in the core functions, which is one way to define it:

julia> rr((5,5), scale=2.0, offset=(1,2))
5×5 IndexFunArray{Float64, 2, IndexFunArrays.var"#g#110"{Float64, Tuple{Int64, Int64}, Tuple{Float64, Float64}, Int64}}:
 2.0      0.0  2.0      4.0       6.0
 2.82843  2.0  2.82843  4.47214   6.32456
 4.47214  4.0  4.47214  5.65685   7.2111
 6.32456  6.0  6.32456  7.2111    8.48528
 8.24621  8.0  8.24621  8.94427  10.0

maybe we should document that better?

[roflmaostc]

Yeah I realized that later.
But wouldn't it be handy to have them in the scaled coordinates?

[roflmaostc]

I guess both has it's pros and cons

[RainerHeintzmann]

There could be a second optional argument "scaled_offset", but then I never had trouble with this since the offset is mostly used with the default options which work OK.

[roflmaostc]

Yeah in my case I wanted to place a gaussian 10 micrometer away from another one...

[roflmaostc]

Please check this commit

That was still a bug, wasn't it?
Now at least if you divide sigma by 10 and also the scaling, it results in the same gaussian

[roflmaostc]

My commit was the intended fix.
Do you think before was correct?

You can test the current master branch

[RainerHeintzmann]

... you are right. The commit fixes it. The confusing thing is that the expression is (abs2.(pos .- offset)) .* scale which makes scale not really a linear scale. Thanks for the fix!
An alternative would be to move scale inside in this expression: abs2(.(pos .- offset).* scale ) and replace the factors appropriately. This might make the code easier to understand?

[RainerHeintzmann]

... since this is a breaking change, we should update the second digit of the version number, right?

[roflmaostc]

It's a bug fix, so I would leave the number the same.

[roflmaostc]

But it's also breaking.
So maybe bumping second digit

[RainerHeintzmann]

Yup, I prefer the second digit. After all all Software using "gaussian" with a scale not 1.0 will need to update sigma to get the same result. Can you bumb and release?

[roflmaostc]

Should we revert this, or not?

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