kingfisher1337 / tensor

just useful dynamic c++ array (tensor) classes

tensor

this is a small c++ program to generate tensor classes up to an arbitrary rank; use the file "tensor.hpp" from this repo or compile "generate-tensor.cpp" yourself to generate "tensor.hpp";

examples:

1. simple 1D-array

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Tensor1 f(10); for (int x = 0; x < 10; ++x) { f(x) = 5.0 * x; }

2. arbitrary index range

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Tensor1 f(-10, +10); for (int x = -10; x <= 10; ++x) { f(x) = 5.0 * x; }

3. multiple indices (non-physicist see wikipedia for the epsilon-tensor or levi-civita-symbol)

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Tensor3 epsilon(1, 3, 1, 3, 1, 3); // each of the 3 epsilon-indices goes from 1 to 3 for (int i = 1; i <= 3; ++i) { for (int j = 1; j <= 3; ++j) { for (int k = 1; k <= 3; ++k) { if (i == j || i == k || j == k) { epsilon(i, j, k) = 0; } else if (i == 1 && j == 2 && k == 3 || i == 2 && j == 3 && k == 1 || i == 3 && j == 1 && k == 2) { epsilon(i, j, k) = 1; } else { epsilon(i, j, k) = -1; } } } }

4. fix first indices

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Tensor2 a(10, 10); for (int i = 0; i < 10; ++i) { for (int j = 0; j < 10; ++j) { a(i, j) = i * j; } } TensorBase1 b = a(5); for (int i = 0; i < 10; ++i) { cout << b(i) << endl; // prints a(5, 0), a(5, 1), ... }

5. get index range

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Tensor2 a(-10, +10, -5, +5); // a(x, y) with -10 <= x <= +10 and -5 <= y +5 int x0 = f.baseIndex(0); int x1 = x0 + f.size(0) - 1; int y0 = f.baseIndex(1); int y1 = y0 + f.size(1) - 1; for (int x = x0; x <= x1; ++x) { for (int y = y0; y <= y1; ++y) { a(x, y) = x + y; } }

6. resize

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Tensor2 a(10, 15); // a(x, y) with 0 <= x < 10 and 0 <= y < 15 ... a.resize(20, 25); // now a(x, y) with 0 <= x < 20 and 0 <= y < 25 ... a.resize(-10, +10, -20, +20); // now a(x, y) with -10 <= x <= +10 and -20 <= x <= +20