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[Octave-bug-tracker] [bug #36732] interp1 does not check input for monot
From: |
Ben Abbott |
Subject: |
[Octave-bug-tracker] [bug #36732] interp1 does not check input for monotonicity |
Date: |
Tue, 21 Aug 2012 23:57:38 +0000 |
User-agent: |
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_7_4) AppleWebKit/536.25 (KHTML, like Gecko) Version/6.0 Safari/536.25 |
Follow-up Comment #56, bug #36732 (project octave):
Regarding Michael's suggestion to use sort() in comment #52 in order to switch
form right to left-continous isn't so straight forward. Consider the example
below, where yR will be right-continous by default.
X = [ 2 1 3 2];
Y = [ 2 1 3 10];
x = 1:0.5:3
yR = interp1 (X, Y, x);
This is equivalent to
yR = interp1 ([1 2 2 3], [1 2 10 3], x)
If sort(..., "descend") is applied to X and Y is modified accordingly we get
...
X = [ 2 1 3 2];
Y = [ 2 1 3 10];
[X, n] = sort (X, "descend")
Which results in
X = 3 2 2 1
n = 3 1 4 2
+verbatim
Using "n" to reorder "Y" results in;
Y = Y(n)
Y = 3 2 10 1
Notice that Y(2) and Y(3) are not what is intended. Meaning, that the example
below still produces a right-continuous result.
X = [ 2 1 3 2];
Y = [ 2 1 3 10];
[~, n] = sort (X, "descend");
x = 1:0.5:3
yR = interp1 (X(n), Y(n), x);
In order the obtain a left-continuous result ...
X = [ 2 1 3 2];
Y = [ 2 1 3 10];
[~, n] = sort (flipud (X), "descend");
x = 1:0.5:3
yL = interp1 (X(n), fliplr(Y)(n), x)
yL =
3.0000 2.5000 2.0000 5.5000 1.0000
yR = interp1 (X, Y, x)
yR =
1.0000 1.5000 10.0000 6.5000 3.0000
My use of fliplr() may be misleading, since internally interp1() operates
along the rows and supports a 2D Y. Meaning, the internal approach to doing
this is different from this example.
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- [Octave-bug-tracker] [bug #36732] interp1 does not check input for monotonicity, (continued)
- [Octave-bug-tracker] [bug #36732] interp1 does not check input for monotonicity, Ben Abbott, 2012/08/20
- [Octave-bug-tracker] [bug #36732] interp1 does not check input for monotonicity, Michael Godfrey, 2012/08/20
- Message not available
- Message not available
- Message not available
- [Octave-bug-tracker] [bug #36732] interp1 does not check input for monotonicity, Ben Abbott, 2012/08/20
- Message not available
- Message not available
- [Octave-bug-tracker] [bug #36732] interp1 does not check input for monotonicity, Ben Abbott, 2012/08/20
- [Octave-bug-tracker] [bug #36732] interp1 does not check input for monotonicity, Michael Godfrey, 2012/08/20
- [Octave-bug-tracker] [bug #36732] interp1 does not check input for monotonicity, Michael Godfrey, 2012/08/21
- [Octave-bug-tracker] [bug #36732] interp1 does not check input for monotonicity, Michael Godfrey, 2012/08/21
- [Octave-bug-tracker] [bug #36732] interp1 does not check input for monotonicity, Michael Godfrey, 2012/08/21
- [Octave-bug-tracker] [bug #36732] interp1 does not check input for monotonicity, Ben Abbott, 2012/08/21
- [Octave-bug-tracker] [bug #36732] interp1 does not check input for monotonicity, Michael Godfrey, 2012/08/21
- [Octave-bug-tracker] [bug #36732] interp1 does not check input for monotonicity,
Ben Abbott <=
- [Octave-bug-tracker] [bug #36732] interp1 does not check input for monotonicity, Edward Meyer, 2012/08/22
- [Octave-bug-tracker] [bug #36732] interp1 does not check input for monotonicity, Ben Abbott, 2012/08/23
- [Octave-bug-tracker] [bug #36732] interp1 does not check input for monotonicity, Ben Abbott, 2012/08/23
- [Octave-bug-tracker] [bug #36732] interp1 does not check input for monotonicity, Michael Godfrey, 2012/08/23
- [Octave-bug-tracker] [bug #36732] interp1 does not check input for monotonicity, Ben Abbott, 2012/08/23
- Re: [Octave-bug-tracker] [bug #36732] interp1 does not check input for monotonicity, Francesco Potortì, 2012/08/19
- Message not available
- Re: [Octave-bug-tracker] [bug #36732] interp1 does not check input for monotonicity, Michael D Godfrey, 2012/08/17