Lesson 14 Usage as temporary objects
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As shown above, static methods as Zero() and Constant() can be used to initialize variables at the time of declaration or at the right-hand side of an assignment operator. You can think of these methods as returning a matrix or array; in fact, they return so-called expression objects which evaluate to a matrix or array when needed, so that this syntax does not incur any overhead.
These expressions can also be used as a temporary object. The second example in the Getting started guide, which we reproduce here, already illustrates this.
m = 94 89.8 43.549.4 101 86.888.3 29.8 37.8m * v =404512261
The expression m + MatrixXf::Constant(3,3,1.2)
constructs the 3-by-3 matrix expression with all its coefficients equal to 1.2 plus the corresponding coefficient of m.
The comma-initializer, too, can also be used to construct temporary objects. The following example constructs a random matrix of size 2-by-3, and then multiplies this matrix on the left with .
0.68 0.566 0.823-0.211 0.597 -0.605-0.211 0.597 -0.605 0.68 0.566 0.823
The finished() method is necessary here to get the actual matrix object once the comma initialization of our temporary submatrix is done.
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