A = 0.0
sets whole array A to zero.
B = C + D
adds C and D then assigns result to B.
A(1) = 0.0
sets one element to zero,
B(0,0) = A(3) + C(5,1)
sets an element of B to the sum of two other elements.
A(2:4) = 0.0
sets A(2), A(3) and A(4) to zero,
B(-1:0,1:2) = C(1:2,2:3) + 1.0
adds one to the subsection of C and assigns to the subsection of B.
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