function[y]=multiplyB(Mesh, Data, x, in)

% multiplyB: Implements the mutiplication between B and a vector x and
% stores the result in y
% INPUT:
% Mesh:     Structure containing all the mesh parameters
% Data:     Structure containing all the data parameters
% x:        Vector or matrix
% in:       Parameter specifiying whether the input is a vector or a matrix
% OUTPUT:
% y:        Result of the multiplication of B with x

if strcmp(in, 'vec')
x=reshape(x, Mesh.nb_dof_local, []);
end

y=zeros(Data.nf,1);

y1=-x*Data.body{1}.interface_mass;
y2=(x*Data.R21')*Data.body{2}.interface_mass;

y(Data.body{1}.indx_local)=y1(:);
y(Data.body{2}.indx_local)=y2(:);
end