Incorrect results of inverse tall array

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chen zhe
chen zhe 2024-6-22
评论： chen zhe 2024-6-22
Ran in:
Hi,
I am using tall array and testing the inverse of A? (pseudo inverse). The system is linear Ax=b. A:245*9, x: 9*1, b:245*1.
However, with the same matrices, the results of gather(A/b) is incorrect, 1st to 7th elements are NaN, 8th is -inf. The last one is the same with non-tall array results.
C = load("C.mat")
C = struct with fields:
dataSitesAugm: [6615x9 double]
C = C.dataSitesAugm;
d = load("d.mat")
d = struct with fields:
functionValues: [6615x1 double]
d = d.functionValues;
A_ds = arrayDatastore([C d], "OutputType","same");
At = tall(A_ds);
A = At(:,1:9);
B1 = At(:,10);
X=A\B1; % solve X in equation A*X=B1
X_1=gather(X)
Evaluating tall expression using the Local MATLAB Session: - Pass 1 of 1: 0% complete - Pass 1 of 1: 9% complete - Pass 1 of 1: 22% complete - Pass 1 of 1: 36% complete - Pass 1 of 1: 50% complete - Pass 1 of 1: 63% complete - Pass 1 of 1: 77% complete - Pass 1 of 1: 91% complete - Pass 1 of 1: Completed in 7.7 sec Evaluation completed in 8.1 sec
X_1 = 9x1
NaN NaN NaN NaN Inf 0.8010 0.6198 0.4161 0.0042
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Y=C\d; % solve X in non-tall array, benchmark
Warning: Rank deficient, rank = 7, tol = 1.194634e-10.
Any one can help this case?
Thanks in advance.

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回答（1 个）

Ayush Modi
Ayush Modi 2024-6-22
Ran in:
Hi Chen,
Your code looks good to me. The issue might be with the data.
I tested the code with randomly generated matrix as well as the attached data. I am able to reproduce the issue with the attached data but is working fine with random data:
% Generate sample data
rng(0);
C = rand(245, 9);
d = rand(245, 1);
data = [C d];
A_ds = arrayDatastore(data, "OutputType", "same");
At = tall(A_ds);
A = At(:, 1:9);
B1 = At(:, 10);
X = A \ B1;
X_1 = gather(X);
Evaluating tall expression using the Local MATLAB Session: - Pass 1 of 1: 0% complete - Pass 1 of 1: Completed in 0.72 sec Evaluation completed in 1.1 sec
Y = C \ d;
disp('Results using tall arrays:');
Results using tall arrays:
disp(X_1);
0.0471 0.1917 0.1769 0.0630 0.0034 0.0588 0.1110 0.0537 0.2454
disp('Results using non-tall arrays:');
Results using non-tall arrays:
disp(Y);
0.0471 0.1917 0.1769 0.0630 0.0034 0.0588 0.1110 0.0537 0.2454
  1 个评论
chen zhe
chen zhe 2024-6-22
Yeah, could be the data issue.
But do you know why the non-tall array works well while the tall array with gather() cannot have the reasonable results?
Not sure if this is a bug.

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