1 test fails - SingularValueDecompositionOctaveTest

[tuxdna]

Originally reported here: https://groups.google.com/forum/?fromgroups=#!topic/s-space-research-dev/Ycy0tWlOnLs

Failed tests: testMatrixReduction(edu.ucla.sspace.matrix.factorization.SingularValueDecompositionOctaveTest): expected:<0.8945379188> but was:<-0.8945360178645925>

[tuxdna]

On further investigation, I found that Octave is actually giving a -ve value i.e. -0.89454. However as per the test-case a +ve value is expected i.e. 0.89454.

$ cat /tmp/svd-octave.dat 1 1 1.0 1 2 1.0 1 7 1.0 2 2 1.0 2 3 1.0 3 1 1.0 4 4 1.0 4 5 1.0 4 6 1.0 5 4 1.0 5 6 1.0 5 7 1.0 $ octave GNU Octave, version 3.2.4 octave:1> Z = load('/tmp/svd-octave.dat','-ascii') warning: load: loaded ASCII file `/tmp/svd-octave.dat' -- ignoring extra args Z =

1 1 1 1 2 1 1 7 1 2 2 1 2 3 1 3 1 1 4 4 1 4 5 1 4 6 1 5 4 1 5 6 1 5 7 1

octave:2> A = spconvert(Z) A =

Compressed Column Sparse (rows = 5, cols = 7, nnz = 12 [34%])

(1, 1) -> 1 (3, 1) -> 1 (1, 2) -> 1 (2, 2) -> 1 (2, 3) -> 1 (4, 4) -> 1 (5, 4) -> 1 (4, 5) -> 1 (4, 6) -> 1 (5, 6) -> 1 (1, 7) -> 1 (5, 7) -> 1

octave:3> clear Z octave:4> [U, S, V] = svds(A, 2) U =

-0.388460 -0.736150 -0.117616 -0.425017 -0.090281 -0.269450 -0.596357 0.425017 -0.686639 0.155567

S =

Diagonal Matrix

2.3028 0 0 1.9319

V =

-0.207897 -0.520537 -0.219768 -0.601064 -0.051076 -0.220005 -0.557152 0.300532 -0.258973 0.220005 -0.557152 0.300532 -0.466871 -0.300532

octave:5> U(1)(1) * S(1) ans = -0.89454

[davidjurgens]

Hi Saleem,

This is interesting! The SVD does not have a unique solution, so it looks like Octave is finding a solution than we expect, with a singular value that has the opposite sign of what we expect. (I suspect the other singular values would have opposite signs as well.) We could potentially revise the unit test so that it checks against the absolute value. Octave's value and the expected value are nearly identical when the sign is ignored, so I think this should work.

Thanks, David

On Thu, May 9, 2013 at 11:09 AM, Saleem Ansari notifications@github.comwrote:

On further investigation, I found that Octave is actually giving a -ve value i.e. -0.89454. However as per the test-case a +ve value is expected i.e. 0.89454.

$ cat /tmp/svd-octave.dat 1 1 1.0 1 2 1.0 1 7 1.0 2 2 1.0 2 3 1.0 3 1 1.0 4 4 1.0 4 5 1.0 4 6 1.0 5 4 1.0 5 6 1.0 5 7 1.0 $ octave GNU Octave, version 3.2.4 octave:1> Z = load('/tmp/svd-octave.dat','-ascii') warning: load: loaded ASCII file `/tmp/svd-octave.dat' -- ignoring extra args Z =

1 1 1 1 2 1 1 7 1 2 2 1 2 3 1 3 1 1 4 4 1 4 5 1 4 6 1 5 4 1 5 6 1 5 7 1

octave:2> A = spconvert(Z) A =

Compressed Column Sparse (rows = 5, cols = 7, nnz = 12 [34%])

(1, 1) -> 1 (3, 1) -> 1 (1, 2) -> 1 (2, 2) -> 1 (2, 3) -> 1 (4, 4) -> 1 (5, 4) -> 1 (4, 5) -> 1 (4, 6) -> 1 (5, 6) -> 1 (1, 7) -> 1 (5, 7) -> 1

octave:3> clear Z octave:4> [U, S, V] = svds(A, 2) U =

-0.388460 -0.736150 -0.117616 -0.425017 -0.090281 -0.269450 -0.596357 0.425017 -0.686639 0.155567

S =

Diagonal Matrix

2.3028 0 0 1.9319

V =

-0.207897 -0.520537 -0.219768 -0.601064 -0.051076 -0.220005 -0.557152 0.300532 -0.258973 0.220005 -0.557152 0.300532 -0.466871 -0.300532

octave:5> U(1)(1) * S(1) ans = -0.89454

— Reply to this email directly or view it on GitHubhttps://github.com/fozziethebeat/S-Space/issues/37#issuecomment-17655750 .

[tuxdna]

Well, in-fact, the signs of expected and actual values sometimes match:

Check U now... r:0, c:0, expected: 0.894538, actual: -0.894536 r:0, c:1, expected: -1.422131, actual: -1.422133 r:1, c:0, expected: 0.270844, actual: -0.270844 r:1, c:1, expected: -0.821069, actual: -0.821069 r:2, c:0, expected: 0.207898, actual: -0.207897 r:2, c:1, expected: -0.520537, actual: -0.520537 r:3, c:0, expected: 1.373279, actual: -1.373277 r:3, c:1, expected: 0.821069, actual: 0.821069 r:4, c:0, expected: 1.581179, actual: -1.581175 r:4, c:1, expected: 0.300532, actual: 0.300532 Check V now... r:0, c:0, expected: 0.478741, actual: -0.478741 r:0, c:1, expected: 0.506077, actual: -0.506076 r:0, c:2, expected: 0.117616, actual: -0.117616 r:0, c:3, expected: 1.282998, actual: -1.282996 r:0, c:4, expected: 0.596358, actual: -0.596357 r:0, c:5, expected: 1.282998, actual: -1.282996 r:0, c:6, expected: 1.075101, actual: -1.075098 r:1, c:0, expected: -1.005599, actual: -1.005600 r:1, c:1, expected: -1.161165, actual: -1.161167 r:1, c:2, expected: -0.425017, actual: -0.425017 r:1, c:3, expected: 0.580583, actual: 0.580584 r:1, c:4, expected: 0.425017, actual: 0.425017 r:1, c:5, expected: 0.580583, actual: 0.580584 r:1, c:6, expected: -0.580583, actual: -0.580584

I don't have an in-depth knowledge of how SVD works. However, if it is safe to ignore the signs of two values, then the test does pass.

[tuxdna]

Closed via https://github.com/fozziethebeat/S-Space/pull/39