How to set the lower bound of extrapolation?

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George McFadden
George McFadden 2012-7-16
评论： charles alexander 2021-7-29
Hi!
Is it possible to set a lower bound for extrapolating using the interp2 function? I am dealing with nitrogen concentrations, and a negative concentration cannot exist. However, currently the extrapolation results have negative values. So I do not want the extrapolation to go less than 0. I do not desire to set an upperbound limit.
Thanks! George
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George McFadden
George McFadden 2012-10-30
The interpolation and extrapolation are both producing below 0 values. Thanks!
charles alexander
charles alexander 2021-7-29
yes, its is possible to set a lower bound.
you will need to find the value of c from the linear discriminant model.
extrapolating will be (c1+c2)/100*values less than 30,
find the percentage value of extrapolation, add the (percentage value to the value of extrapolation:c3).
(c1+c2)/c3*fill_value.

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D G
D G 2012-7-16
You could set the boundary limit manually after the calculation like this.
concentration(concentration < 0) = 0;
I create a function that does just this.
function value = clip(value, clip, type)
%CLIP Clip values
% Adjust values in a vector such that no value extends beyond the
% specified type.
%
% Inputs:
% Clip min and max together:
% value (vector - 1 by x)
% clip (vector - 1 by x > 1)
% Clip min and max seperately
% value (vector - 1 by x)
% clip (scalar)
% type (char - min/max)
%
% Outputs:
% value - The clipped values
if length(clip) > 1
value(max(clip) < value) = max(clip);
value(value < min(clip)) = min(clip);
else
switch lower(type)
case 'min'
value(value < clip) = clip;
case 'max'
value(clip < value) = clip;
end %switch
end
end %clip
And you can use it like this.
concentration = clip(concentration, 0, 'min');
But it is more useful when you want to clip on both ends of the spectrum.
concentration = clip(concentration, [0, 100]);
If you have more than 2 values in the boundary, it choose the min and max as the clipping boundaries.
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Walter Roberson
Walter Roberson 2012-7-17
concentration(concentration < 0) = 0;
can also be formulated as
concentration = max(0, concentration);
D G
D G 2012-7-17
编辑：D G 2012-7-17
So it can, hilarious! It seems a little backwards. Why wouldn't that be min, and the reverse be max?
http://www.youtube.com/watch?v=JyV96ZpJG98#t=04m23s

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