Intrinsic matrix math
| Sum and product | |
| Matmul | |
| Transpose | |
| Reshape |
Sum and product
Sum and product reduce a whole array to one number. Add a mask to skip the elements you do not want. The mask must have the same shape as the array.
program sum_demo
implicit none
real :: a(4) = [1.0, 2.0, 3.0, 4.0]
print *, sum(a)
print *, product(a)
print *, sum(a, mask = a > 0.0)
end program sum_demo
Matmul
Matmul multiplies two matrices or a matrix with a vector. The inner sizes must agree: an (m, k) array times a (k, n) array gives an (m, n) array. Check shapes before the call to avoid a runtime error.
program mm_demo
implicit none
real :: a(2, 2) = reshape([1.0, 2.0, 3.0, 4.0], [2, 2])
real :: b(2, 2) = reshape([5.0, 6.0, 7.0, 8.0], [2, 2])
real :: c(2, 2)
c = matmul(a, b)
print *, c
end program mm_demo
Transpose
Transpose flips rows and columns. The result of transposing a (2, 3) array is a (3, 2) array, so declare the target with swapped bounds.
program transpose_demo
implicit none
real :: a(2, 3) = reshape([1.0, 2.0, 3.0, 4.0, 5.0, 6.0], [2, 3])
real :: b(3, 2)
b = transpose(a)
print *, b
end program transpose_demo
Reshape
Reshape packs flat data into any conformable shape. Shape reports the extents and size reports the element count. Use them together when a dummy argument accepts any shape.
program reshape_demo
implicit none
real :: v(6) = [1.0, 2.0, 3.0, 4.0, 5.0, 6.0]
real :: m(2, 3)
m = reshape(v, [2, 3])
print *, shape(m)
print *, size(m)
end program reshape_demo
Next: Random numbers
Article author: Arthur Isaev
