Feat: Modify matmul to support SimpleArray of 1 dimension and 2 dimension #661

ThreeMonth03 · 2026-01-19T09:06:42Z

Problem

There are some __matmul__ operations in Kalman Filter. However, the current design only supports the arguments of 2 dimensions SimpleArray. If we want to matrix multiply from 2 dimensions SimpleArray to 1 dimension SimpleArray, we should reshape the SimpleArray twice. The detail of the discussion could be found in #601 .

void KalmanFilter<T>::predict_state()
{
    // x <- F x  (m_x <- m_f @ m_x)
    array_type x_col = m_x.reshape(small_vector<size_t>{m_state_size, 1});
    x_col = m_f.matmul(x_col);
    m_x = x_col.reshape(small_vector<size_t>{m_state_size});
    m_x = m_f.matmul(m_x);
}

Solution

In this pull request, I modify __matmul__ operation, so that it can support the following number of dimension of SimpleArray:

1D x 1D
1D x 2D
2D x 1D
2D x 2D

ThreeMonth03

@yungyuc Please review this pull request. Thank you.

ThreeMonth03 · 2026-01-19T10:07:29Z

cpp/modmesh/buffer/SimpleArray.hpp

+    bool other_is_1d = (other_ndim == 1);

-    if (k != other.shape(0))
+    if (this_is_1d && other_is_1d)


The condition looks verbose. However, the input argument should be constant value, and if we try to reshape the input argument to another SimpleArry, the assignment operator would clone the buffer.

ThreeMonth03 · 2026-01-19T10:07:45Z

cpp/modmesh/linalg/kalman_filter.hpp

-    array_type x_col = m_x.reshape(small_vector<size_t>{m_state_size, 1});
-    array_type u_col = u.reshape(small_vector<size_t>{m_control_size, 1});
-    x_col = m_f.matmul(x_col).add(m_b.matmul(u_col));
-    m_x = x_col.reshape(small_vector<size_t>{m_state_size});
+    m_x = m_f.matmul(m_x).add(m_b.matmul(u));


Simplify the logic.

tigercosmos · 2026-01-19T16:32:46Z

cpp/modmesh/buffer/SimpleArray.hpp

-    result.fill(static_cast<value_type>(0));
-
-    for (size_t i = 0; i < m; ++i)
+    else if (this_is_1d)


I will add a comment for "1D x 2D"

tigercosmos · 2026-01-19T16:33:06Z

cpp/modmesh/buffer/SimpleArray.hpp

+        }
+        return result;
+    }
+    else if (other_is_1d)


I would leave a comment "2D x 1D".

tigercosmos · 2026-01-19T16:34:01Z

cpp/modmesh/buffer/SimpleArray.hpp

+        check_product_shape(athis, &other, 0, 0);
+        shape_type result_shape{n};
+        A result(result_shape);
+        result.fill(static_cast<value_type>(0));


No need? Any element will not be modified later?

SimpleArray is constructed by std::malloc, which doesn't initialize the buffer. Furthermore, the elements are multiplied and added in the following for loop, so it is necessary to filled 0 in SimpleArray.

modmesh/cpp/modmesh/buffer/ConcreteBuffer.hpp

Lines 294 to 297 in 2a316f4

else

{

ptr = std::malloc(nbytes);

}

This zero-initialization loop should be removed by using a temporary scalar for the inner loop below.

for (size_t j = 0; j < n; ++j) { T v = 0.0; for (size_t l = 0; l < k; ++l) { v += (*athis)(l)*other(l, j); } result.data(j); }

tigercosmos · 2026-01-19T16:34:23Z

cpp/modmesh/buffer/SimpleArray.hpp

    }

-    return result;
+    return {};


I will let it throw here as it should never reach here.

yungyuc

Good enhancement. Points to address:

Update code comments for dimension order.
Update error messages for dimension order.
Remove the zero-initialization loop by using a temporary scalar for the inner loop below.
Write informative summary in the commit log.

yungyuc · 2026-01-20T14:28:51Z

cpp/modmesh/buffer/SimpleArray.hpp

- * Perform matrix multiplication for 2D arrays.
- * This implementation supports only 2D x 2D matrix multiplication.
+ * Perform matrix multiplication for SimpleArrays.
+ * This implementation supports 2D x 2D, 2D x 1D, 1D x 2D, and 1D x 1D matrix multiplication.


List the dimension from low to high: 1D x 1D, 1D x 2D, 2D x 1D, 2D x 2D.

yungyuc · 2026-01-20T14:30:15Z

cpp/modmesh/buffer/SimpleArray.hpp

    {
        const std::string err = std::format("SimpleArray::matmul(): unsupported dimensions: "
-                                            "this={} other={}. Only 2D x 2D matrix multiplication is supported",
+                                            "this={} other={}. SimpleArray must be 2D or 1D.",


Order dimension in the error message from low to high: 1D or 2D.

yungyuc · 2026-01-20T14:32:19Z

cpp/modmesh/buffer/SimpleArray.hpp

+        check_product_shape(athis, &other, 0, 0);
+        shape_type result_shape{n};
+        A result(result_shape);
+        result.fill(static_cast<value_type>(0));


This zero-initialization loop should be removed by using a temporary scalar for the inner loop below.

for (size_t j = 0; j < n; ++j) { T v = 0.0; for (size_t l = 0; l < k; ++l) { v += (*athis)(l)*other(l, j); } result.data(j); }

ThreeMonth03

Good enhancement. Points to address:

Update code comments for dimension order.

Update error messages for dimension order.

Remove the zero-initialization loop by using a temporary scalar for the inner loop below.

Write informative summary in the commit log.

@yungyuc Please review again. Thanks.

yungyuc

Clarify why static_cast is needed for value initialization instead of just value_type v = 0.

yungyuc · 2026-01-24T04:33:35Z

cpp/modmesh/buffer/SimpleArray.hpp

+
        for (size_t j = 0; j < n; ++j)
        {
+            value_type v = static_cast<value_type>(0);


Why do you need to write value_type v = static_cast<value_type>(0); instead of just:

value_type v = 0;

Yes, we don't need to explicitly cast here, and I will fix it.

…ul() to support the argument of 1 dimensional and 2 dimensional SimpleArray

ThreeMonth03 · 2026-01-24T10:45:35Z

cpp/modmesh/buffer/SimpleArray.hpp

+
        for (size_t j = 0; j < n; ++j)
        {
+            value_type v = 0;


ThreeMonth03 commented Jan 19, 2026

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tigercosmos reviewed Jan 19, 2026

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ThreeMonth03 force-pushed the 2Dby1D branch 3 times, most recently from 355d5c0 to eb7d443 Compare January 20, 2026 07:11

yungyuc requested changes Jan 20, 2026

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yungyuc assigned ThreeMonth03 Jan 20, 2026

yungyuc added the array Multi-dimensional array implementation label Jan 20, 2026

ThreeMonth03 force-pushed the 2Dby1D branch 3 times, most recently from 2015d49 to 3cb8236 Compare January 21, 2026 11:04

ThreeMonth03 commented Jan 21, 2026

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ThreeMonth03 requested a review from yungyuc January 21, 2026 11:56

yungyuc requested changes Jan 24, 2026

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Feat SimpleArray.hpp, kalman_filter.hpp and test_gemm.py: Modify matm…

3983fc8

…ul() to support the argument of 1 dimensional and 2 dimensional SimpleArray

ThreeMonth03 force-pushed the 2Dby1D branch from 3cb8236 to 3983fc8 Compare January 24, 2026 09:19

ThreeMonth03 requested a review from yungyuc January 24, 2026 10:45

ThreeMonth03 commented Jan 24, 2026

View reviewed changes

cpp/modmesh/buffer/SimpleArray.hpp

for (size_t j = 0; j < n; ++j)

{

value_type v = 0;

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ThreeMonth03 Jan 24, 2026

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Fixed.

Feat: Modify __matmul__ to support SimpleArray of 1 dimension and 2 dimension #661

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Feat: Modify __matmul__ to support SimpleArray of 1 dimension and 2 dimension #661

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ThreeMonth03 commented Jan 19, 2026

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Feat: Modify matmul to support SimpleArray of 1 dimension and 2 dimension #661

Feat: Modify matmul to support SimpleArray of 1 dimension and 2 dimension #661

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