added slice example

Former-commit-id: a6348be72dd96826ae8fa21450ec04aa2d6585e7

examples/slice/Makefile

@@ -0,0 +1,24 @@
+
+.PHONY: all
+
+all: example
+
+.PHONY: example
+
+igl_lib=-I../../
+eigen=-I/usr/local/include/eigen3 -I/usr/local/include/eigen3/unsupported
+
+#CFLAGS=-g
+CFLAGS=-Os -DNDEBUG
+inc=$(igl_lib) $(eigen)
+lib=
+
+example: example.o
+	g++ $(CFLAGS) -o example example.o $(lib)
+	rm example.o
+
+example.o: example.cpp
+	g++ $(CFLAGS) -c example.cpp -o example.o $(inc)
+clean:
+	rm -f example.o
+	rm -f example

examples/slice/README

@@ -0,0 +1,8 @@
+Small example showing how to use the slice.h function in the igl lib which is
+like the slice operator in matlab.
+
+Compile:
+  make
+
+Run:
+  ./example

examples/slice/example.cpp

@@ -0,0 +1,47 @@
+#include <Eigen/Dense>
+#define EIGEN_YES_I_KNOW_SPARSE_MODULE_IS_NOT_STABLE_YET
+#define EIGEN_IM_MAD_AS_HELL_AND_IM_NOT_GOING_TO_TAKE_IT_ANYMORE
+#include <Eigen/Sparse>
+using namespace Eigen;
+
+#include <cstdio>
+#include <iostream>
+using namespace std;
+
+#include "slice.h"
+#include "speye.h"
+#include "print_ijv.h"
+using namespace igl;
+
+int main(int argc, char * argv[])
+{
+  // Dense
+  MatrixXd A = MatrixXd::Identity(5,5);
+  cout<<"A=["<<endl<<A<<endl<<"];"<<endl;
+  // Row and column indices
+  MatrixXi R(6,1);
+  R<<0,1,2,4,4,0;
+  cout<<"R=["<<endl<<R<<endl<<"];"<<endl;
+  MatrixXi C(4,1);
+  C<<2,2,4,0;
+  cout<<"C=["<<endl<<C<<endl<<"];"<<endl;
+  MatrixXd B;
+  cout<<"B=A(R,C);"<<endl;
+  slice(A,R,C,B);
+  cout<<"B=["<<endl<<B<<endl<<"];"<<endl;
+  
+  cout<<endl;
+
+  //SparseMatrix
+  SparseMatrix<double> spA;
+  speye(5,5,spA);
+  cout<<"spA_IJV=["<<endl;print_ijv(spA,1);cout<<endl<<"];"<<endl;
+  cout<<"spA=sparse(spA_IJV(:,1),spA_IJV(:,2),spA_IJV(:,3));"<<endl;
+  SparseMatrix<double> spB;
+  cout<<"spB=spA(R,C);"<<endl;
+  slice(spA,R,C,spB);
+  cout<<"spB_IJV=["<<endl;print_ijv(spB,1);cout<<endl<<"];"<<endl;
+  cout<<"spB=sparse(spB_IJV(:,1),spB_IJV(:,2),spB_IJV(:,3));"<<endl;
+
+  return 0;
+}