Gradient and NaN
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回答（2 个）
Matt Fig
2011-1-24
You can see what MATLAB does by looking at a plot. Look at the difference between the two figures:
v = -2:0.5:2;
[x,y] = meshgrid(v);
z = x .* exp(-x.^2 - y.^2);
[px,py] = gradient(z,.5,.5);
quiver(v,v,px,py),
z(5,5) = nan; % Set the central data to nan.
[px2,py2] = gradient(z,.2,.2);
figure
quiver(v,v,px2,py2)
Walter Roberson
2011-1-25
>> [fx,fy] = gradient([1 nan 3;5 9 15])
fx =
NaN 1 NaN
4 5 6
fy =
4 NaN 12
4 NaN 12
In other words, any location whose value would involve using the nan in the calculation, gets calculated as nan. Which is the result you would expect if the routine did simple arithmetic operations without any checking for nan.
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