62 lines
2.7 KiB
C++
62 lines
2.7 KiB
C++
#include <Eigen/Array>
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int main(int argc, char *argv[]) {
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std::cout.precision(2);
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// demo static functions
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Eigen::Matrix3f m3 = Eigen::Matrix3f::Random();
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Eigen::Matrix4f m4 = Eigen::Matrix4f::Identity();
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std::cout << "*** Step 1 ***\nm3:\n" << m3 << "\nm4:\n" << m4 << std::endl;
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// demo non-static set... functions
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m4.setZero();
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m3.diagonal().setOnes();
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std::cout << "*** Step 2 ***\nm3:\n" << m3 << "\nm4:\n" << m4 << std::endl;
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// demo fixed-size block() expression as lvalue and as rvalue
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m4.block<3, 3>(0, 1) = m3;
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m3.row(2) = m4.block<1, 3>(2, 0);
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std::cout << "*** Step 3 ***\nm3:\n" << m3 << "\nm4:\n" << m4 << std::endl;
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// demo dynamic-size block()
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{
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int rows = 3, cols = 3;
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m4.block(0, 1, 3, 3).setIdentity();
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std::cout << "*** Step 4 ***\nm4:\n" << m4 << std::endl;
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}
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// demo vector blocks
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m4.diagonal().block(1, 2).setOnes();
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std::cout << "*** Step 5 ***\nm4.diagonal():\n" << m4.diagonal() << std::endl;
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std::cout << "m4.diagonal().start(3)\n" << m4.diagonal().start(3) << std::endl;
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// demo coeff-wise operations
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m4 = m4.cwise() * m4;
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m3 = m3.cwise().cos();
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std::cout << "*** Step 6 ***\nm3:\n" << m3 << "\nm4:\n" << m4 << std::endl;
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// sums of coefficients
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std::cout << "*** Step 7 ***\n m4.sum(): " << m4.sum() << std::endl;
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std::cout << "m4.col(2).sum(): " << m4.col(2).sum() << std::endl;
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std::cout << "m4.colwise().sum():\n" << m4.colwise().sum() << std::endl;
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std::cout << "m4.rowwise().sum():\n" << m4.rowwise().sum() << std::endl;
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// demo intelligent auto-evaluation
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m4 = m4 * m4; // auto-evaluates so no aliasing problem (performance penalty is low)
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Eigen::Matrix4f other = (m4 * m4).lazy(); // forces lazy evaluation
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m4 = m4 + m4; // here Eigen goes for lazy evaluation, as with most expressions
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m4 = -m4 + m4 + 5 * m4; // same here, Eigen chooses lazy evaluation for all that.
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m4 = m4 * (m4 + m4); // here Eigen chooses to first evaluate m4 + m4 into a temporary.
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// indeed, here it is an optimization to cache this intermediate result.
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m3 = m3 * m4.block<3, 3>(1, 1); // here Eigen chooses NOT to evaluate block() into a temporary
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// because accessing coefficients of that block expression is not more costly than
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// accessing coefficients of a plain matrix.
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m4 = m4 * m4.transpose(); // same here, lazy evaluation of the transpose.
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m4 = m4 * m4.transpose().eval(); // forces immediate evaluation of the transpose
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std::cout << "*** Step 8 ***\nm3:\n" << m3 << "\nm4:\n" << m4 << std::endl;
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}
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