In [4]:

    

using Plots
default(size=(500,300))
n = 1000
a = rand(n)
y = Float64[i*a[i]+j*a[j] for i in 1:n, j in 1:n]
y = float(y .> mean(y));


    

In [5]:

    

spy(y, nbins=(20,100))


    

    




 





    
Out[5]:

In [6]:

    

spy(y, nbins=n)


    

    




       legend: false
      linetype: heatmap
         nbins: (20,100)
         yflip: true


 





    
Out[6]:












    




       legend: false
      linetype: heatmap
         nbins: 1000
         yflip: true

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# get the indices (I,J) and the values (V) of non-zero values in y
I,J,V = findnz(y);
# plot the J's vs the I's in a heatmap to recreate the spy call
heatmap(J,I)


    

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pyplot()


    

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histogram(randn(1000),


    

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