在MATLAB中如何获取矩阵的指数？

Question

I have a MATLAB code which I have to convert to C language. According to the MATLAB code,

n1 = 11; x1 = randn(2,n1) + repmat([-1 1]’,1,n1);
w = [0 0]’; 

here acccording to my calculation, the output of

w’*x1

will be a 1x3 matrix, that is a row vector as far as I know.

Then what will be the output of the following code,

z = exp(repmat(b,1,n1)+w’*x1);

where repmat() also creates a 1xn1 matrix (I'm not sure about this, figured it out from manual). My understanding is that addition of two 1x3 matrices will not give a scalar.

How is an exponential is taken here? Can exponential be applied to a matrix?

Answer 1

Like many MATLAB functions, the exp function operates element-wise when applied to arrays. For further details, please refer to the documentation .

Answer 2

Yes, you can apply exponentation to a matrix. From the Wikipedia article: Matrix exponential

Let X be an n×n real or complex matrix. The exponential of X, denoted by e ^X or exp(X), is the n×n matrix given by the power series

e^X = Sum(k=0, infinity) 1/k! * X^k 

As @John Bartholomew pointed though, this is not what the exp() of Matlab does.