title: dlib krr_trainer gives error on multidimensional data
body: <p>I am trying out dlib for a problem. Given the area of house and no of trees in the locality, the price of the house is provided. We wish to predict the price of the house using krr trainer for a given area and no Of Trees</p>
  
  <pre><code>area , noOfTrees, priceOFHouse
  100 , 10 , 400
  100 ,50, 2000
  200 , 1,200
  .... lots more
  </code></pre>
  
  <p>I planned to use kernel ridge regression </p>
  
  <pre><code>typedef matrix&lt;double, 2, 1&gt; sample_type;
  typedef radial_basis_kernel&lt;sample_type&gt; kernel_type;
  krr_trainer&lt;kernel_type&gt; trainer;
  
  // i took trainign data and put htose data in 2 vectors 
  //  std::vector&lt;std::vector&lt;double&gt; &gt; feactureVector;
  //  std::vector&lt;double&gt; resultVector;
  populateTrainigData(feactureVector, resultVector) ; 
  // so featurevector[0] is {100,10} resultvector[0] is 400 
  decision_function&lt;kernel_type&gt;  test = trainer.train(feactureVector, resultVector);
  
  sample_type m;
  m(0, 0) = 100; // area of house is 100 
  m(1, 0) = 25; // no of treess in neighbourhood is 25 
  
  double result = test(m);
  </code></pre>
  
  <p>At line <code>decision_function&lt;kernel_type&gt;  test</code> it gives compile error . </p>
  
  <pre><code>d:\dlib-19.15\dlib\svm\krr_trainer.h(300): error C2664: 'const dlib::matrix&lt;double,0,1,dlib::default_memory_manager,dlib::row_major_layout&gt; &amp;dlib::empirical_kernel_map&lt;dlib::radial_basis_kernel&lt;sample_type&gt;&gt;::project(const dlib::matrix&lt;T,2,1,dlib::default_memory_manager,dlib::row_major_layout&gt; &amp;,double &amp;) const': cannot convert argument 1 from 'const std::vector&lt;double,std::allocator&lt;_Ty&gt;&gt;' to 'const dlib::matrix&lt;T,2,1,dlib::default_memory_manager,dlib::row_major_layout&gt; &amp;'
  1&gt; 
  </code></pre>
  
  <p>Can someone point me in the right direction where I can solve this problem as the example on the dlib site shows only a single dimension example. I am using that as a reference guide and the error &amp; system is strange to me.</p>