Section: Mathematical Operators
y = a .* b
where a and b are n-dimensional arrays of numerical type. In the
first case, the two arguments are the same size, in which case, the
output y is the same size as the inputs, and is the element-wise
product of a and b. In the second case, either a or b is a scalar,
in which case y is the same size as the larger argument,
and is the product of the scalar with each element of the other argument.
The type of y depends on the types of a and b using type
promotion rules. All of the types are preserved under multiplication except
for integer types, which are promoted to int32 prior to
multiplication (same as C).
If a is a scalar, then the output is computed via
On the other hand, if b is a scalar, then the output is computed via
.* operator. The first example
is straightforward:
--> 3 .* 8 ans = 24
Note, however, that because of the way that input is parsed, eliminating
the spaces 3.*8 results in the input being parsed as 3. * 8,
which yields a double result:
--> 3.*8 ans = 24
This is really an invokation of the times operator.
Next, we use the floating point syntax to force one of the arguments
to be a double, which results in the output being double:
--> 3.1 .* 2
ans =
6.2000
Note that if one of the arguments is complex-valued, the output will be complex also.
--> a = 3 + 4*i
a =
3.0000 + 4.0000i
--> b = a .* 2.0f
b =
6.0000 + 8.0000i
If a complex value is multiplied by a double, the result is
promoted to dcomplex.
--> b = a .* 2.0
b =
6.0000 + 8.0000i
We can also demonstrate the three forms of the dottimes operator. First the element-wise version:
--> a = [1,2;3,4] a = 1 2 3 4 --> b = [2,3;6,7] b = 2 3 6 7 --> c = a .* b c = 2 6 18 28
Then the scalar versions
--> c = a .* 3 c = 3 6 9 12 --> c = 3 .* a c = 3 6 9 12