examples/example1.cpp

@@ -0,0 +1,154 @@
+#include <iostream>
+#include <armadillo>
+
+using namespace std;
+using namespace arma;
+
+// Armadillo documentation is available at:
+// http://arma.sourceforge.net/docs.html
+
+// NOTE: the C++11 "auto" keyword is not recommended for use with Armadillo objects and functions
+
+int
+main(int argc, char** argv)
+  {
+  cout << "Armadillo version: " << arma_version::as_string() << endl;
+  
+  mat A(2,3);  // directly specify the matrix size (elements are uninitialised)
+  
+  cout << "A.n_rows: " << A.n_rows << endl;  // .n_rows and .n_cols are read only
+  cout << "A.n_cols: " << A.n_cols << endl;
+  
+  A(1,2) = 456.0;  // directly access an element (indexing starts at 0)
+  A.print("A:");
+  
+  A = 5.0;         // scalars are treated as a 1x1 matrix
+  A.print("A:");
+  
+  A.set_size(4,5); // change the size (data is not preserved)
+  
+  A.fill(5.0);     // set all elements to a particular value
+  A.print("A:");
+  
+  // endr indicates "end of row"
+  A << 0.165300 << 0.454037 << 0.995795 << 0.124098 << 0.047084 << endr
+    << 0.688782 << 0.036549 << 0.552848 << 0.937664 << 0.866401 << endr
+    << 0.348740 << 0.479388 << 0.506228 << 0.145673 << 0.491547 << endr
+    << 0.148678 << 0.682258 << 0.571154 << 0.874724 << 0.444632 << endr
+    << 0.245726 << 0.595218 << 0.409327 << 0.367827 << 0.385736 << endr;
+  
+  A.print("A:");
+  
+  // determinant
+  cout << "det(A): " << det(A) << endl;
+  
+  // inverse
+  cout << "inv(A): " << endl << inv(A) << endl;
+  
+  // save matrix as a text file
+  A.save("A.txt", raw_ascii);
+  
+  // load from file
+  mat B;
+  B.load("A.txt");
+  
+  // submatrices
+  cout << "B( span(0,2), span(3,4) ):" << endl << B( span(0,2), span(3,4) ) << endl;
+  
+  cout << "B( 0,3, size(3,2) ):" << endl << B( 0,3, size(3,2) ) << endl;
+  
+  cout << "B.row(0): " << endl << B.row(0) << endl;
+  
+  cout << "B.col(1): " << endl << B.col(1) << endl;
+  
+  // transpose
+  cout << "B.t(): " << endl << B.t() << endl;
+  
+  // maximum from each column (traverse along rows)
+  cout << "max(B): " << endl << max(B) << endl;
+  
+  // maximum from each row (traverse along columns)
+  cout << "max(B,1): " << endl << max(B,1) << endl;
+  
+  // maximum value in B
+  cout << "max(max(B)) = " << max(max(B)) << endl;
+  
+  // sum of each column (traverse along rows)
+  cout << "sum(B): " << endl << sum(B) << endl;
+  
+  // sum of each row (traverse along columns)
+  cout << "sum(B,1) =" << endl << sum(B,1) << endl;
+  
+  // sum of all elements
+  cout << "accu(B): " << accu(B) << endl;
+  
+  // trace = sum along diagonal
+  cout << "trace(B): " << trace(B) << endl;
+  
+  // generate the identity matrix
+  mat C = eye<mat>(4,4);
+  
+  // random matrix with values uniformly distributed in the [0,1] interval
+  mat D = randu<mat>(4,4);
+  D.print("D:");
+  
+  // row vectors are treated like a matrix with one row
+  rowvec r;
+  r << 0.59119 << 0.77321 << 0.60275 << 0.35887 << 0.51683;
+  r.print("r:");
+  
+  // column vectors are treated like a matrix with one column
+  vec q;
+  q << 0.14333 << 0.59478 << 0.14481 << 0.58558 << 0.60809;
+  q.print("q:");
+  
+  // convert matrix to vector; data in matrices is stored column-by-column
+  vec v = vectorise(A);
+  v.print("v:");
+  
+  // dot or inner product
+  cout << "as_scalar(r*q): " << as_scalar(r*q) << endl;
+  
+  // outer product
+  cout << "q*r: " << endl << q*r << endl;
+  
+  // multiply-and-accumulate operation (no temporary matrices are created)
+  cout << "accu(A % B) = " << accu(A % B) << endl;
+  
+  // example of a compound operation
+  B += 2.0 * A.t();
+  B.print("B:");
+  
+  // imat specifies an integer matrix
+  imat AA;
+  imat BB;
+  
+  AA << 1 << 2 << 3 << endr << 4 << 5 << 6 << endr << 7 << 8 << 9;
+  BB << 3 << 2 << 1 << endr << 6 << 5 << 4 << endr << 9 << 8 << 7;
+  
+  // comparison of matrices (element-wise); output of a relational operator is a umat
+  umat ZZ = (AA >= BB);
+  ZZ.print("ZZ:");
+  
+  // cubes ("3D matrices")
+  cube Q( B.n_rows, B.n_cols, 2 );
+  
+  Q.slice(0) = B;
+  Q.slice(1) = 2.0 * B;
+  
+  Q.print("Q:");
+  
+  // 2D field of matrices; 3D fields are also supported
+  field<mat> F(4,3); 
+  
+  for(uword col=0; col < F.n_cols; ++col)
+  for(uword row=0; row < F.n_rows; ++row)
+    {
+    F(row,col) = randu<mat>(2,3);  // each element in field<mat> is a matrix
+    }
+  
+  F.print("F:");
+  
+  return 0;
+  }
+