xref: /aosp_15_r20/external/eigen/doc/tutorial.cpp (revision bf2c37156dfe67e5dfebd6d394bad8b2ab5804d4)
1*bf2c3715SXin Li #include <Eigen/Array>
2*bf2c3715SXin Li 
main(int argc,char * argv[])3*bf2c3715SXin Li int main(int argc, char *argv[])
4*bf2c3715SXin Li {
5*bf2c3715SXin Li   std::cout.precision(2);
6*bf2c3715SXin Li 
7*bf2c3715SXin Li   // demo static functions
8*bf2c3715SXin Li   Eigen::Matrix3f m3 = Eigen::Matrix3f::Random();
9*bf2c3715SXin Li   Eigen::Matrix4f m4 = Eigen::Matrix4f::Identity();
10*bf2c3715SXin Li 
11*bf2c3715SXin Li   std::cout << "*** Step 1 ***\nm3:\n" << m3 << "\nm4:\n" << m4 << std::endl;
12*bf2c3715SXin Li 
13*bf2c3715SXin Li   // demo non-static set... functions
14*bf2c3715SXin Li   m4.setZero();
15*bf2c3715SXin Li   m3.diagonal().setOnes();
16*bf2c3715SXin Li 
17*bf2c3715SXin Li   std::cout << "*** Step 2 ***\nm3:\n" << m3 << "\nm4:\n" << m4 << std::endl;
18*bf2c3715SXin Li 
19*bf2c3715SXin Li   // demo fixed-size block() expression as lvalue and as rvalue
20*bf2c3715SXin Li   m4.block<3,3>(0,1) = m3;
21*bf2c3715SXin Li   m3.row(2) = m4.block<1,3>(2,0);
22*bf2c3715SXin Li 
23*bf2c3715SXin Li   std::cout << "*** Step 3 ***\nm3:\n" << m3 << "\nm4:\n" << m4 << std::endl;
24*bf2c3715SXin Li 
25*bf2c3715SXin Li   // demo dynamic-size block()
26*bf2c3715SXin Li   {
27*bf2c3715SXin Li     int rows = 3, cols = 3;
28*bf2c3715SXin Li     m4.block(0,1,3,3).setIdentity();
29*bf2c3715SXin Li     std::cout << "*** Step 4 ***\nm4:\n" << m4 << std::endl;
30*bf2c3715SXin Li   }
31*bf2c3715SXin Li 
32*bf2c3715SXin Li   // demo vector blocks
33*bf2c3715SXin Li   m4.diagonal().block(1,2).setOnes();
34*bf2c3715SXin Li   std::cout << "*** Step 5 ***\nm4.diagonal():\n" << m4.diagonal() << std::endl;
35*bf2c3715SXin Li   std::cout << "m4.diagonal().start(3)\n" << m4.diagonal().start(3) << std::endl;
36*bf2c3715SXin Li 
37*bf2c3715SXin Li   // demo coeff-wise operations
38*bf2c3715SXin Li   m4 = m4.cwise()*m4;
39*bf2c3715SXin Li   m3 = m3.cwise().cos();
40*bf2c3715SXin Li   std::cout << "*** Step 6 ***\nm3:\n" << m3 << "\nm4:\n" << m4 << std::endl;
41*bf2c3715SXin Li 
42*bf2c3715SXin Li   // sums of coefficients
43*bf2c3715SXin Li   std::cout << "*** Step 7 ***\n m4.sum(): " << m4.sum() << std::endl;
44*bf2c3715SXin Li   std::cout << "m4.col(2).sum(): " << m4.col(2).sum() << std::endl;
45*bf2c3715SXin Li   std::cout << "m4.colwise().sum():\n" << m4.colwise().sum() << std::endl;
46*bf2c3715SXin Li   std::cout << "m4.rowwise().sum():\n" << m4.rowwise().sum() << std::endl;
47*bf2c3715SXin Li 
48*bf2c3715SXin Li   // demo intelligent auto-evaluation
49*bf2c3715SXin Li   m4 = m4 * m4; // auto-evaluates so no aliasing problem (performance penalty is low)
50*bf2c3715SXin Li   Eigen::Matrix4f other = (m4 * m4).lazy(); // forces lazy evaluation
51*bf2c3715SXin Li   m4 = m4 + m4; // here Eigen goes for lazy evaluation, as with most expressions
52*bf2c3715SXin Li   m4 = -m4 + m4 + 5 * m4; // same here, Eigen chooses lazy evaluation for all that.
53*bf2c3715SXin Li   m4 = m4 * (m4 + m4); // here Eigen chooses to first evaluate m4 + m4 into a temporary.
54*bf2c3715SXin Li                        // indeed, here it is an optimization to cache this intermediate result.
55*bf2c3715SXin Li   m3 = m3 * m4.block<3,3>(1,1); // here Eigen chooses NOT to evaluate block() into a temporary
56*bf2c3715SXin Li     // because accessing coefficients of that block expression is not more costly than accessing
57*bf2c3715SXin Li     // coefficients of a plain matrix.
58*bf2c3715SXin Li   m4 = m4 * m4.transpose(); // same here, lazy evaluation of the transpose.
59*bf2c3715SXin Li   m4 = m4 * m4.transpose().eval(); // forces immediate evaluation of the transpose
60*bf2c3715SXin Li 
61*bf2c3715SXin Li   std::cout << "*** Step 8 ***\nm3:\n" << m3 << "\nm4:\n" << m4 << std::endl;
62*bf2c3715SXin Li }
63