Add warning for single placement in analyze methods

doc/md/dispersion.md

@@ -2,7 +2,7 @@
 
 The command takes a set of `jplace` files, and calculates and visualizes the Edge Dispersion per edge of the reference tree. The files need to have the same reference tree.
 
-Edge Dispersion is explained and evaluated in detail in our article (in preparation). The following figure and its caption are an example adapted from this article:
+Edge Dispersion is explained and evaluated in detail in our article (doi:[10.1371/journal.pone.0217050](https://doi.org/10.1371/journal.pone.0217050)). The following figure and its caption are an example adapted from this article:
 
 <br>
 

src/commands/analyze/correlation.cpp

@@ -435,6 +435,14 @@ void run_correlation( CorrelationOptions const& options )
 
     // Get the data. Read all samples and calcualte the matrices.
     auto const profile = options.jplace_input.placement_profile();
+    assert( profile.edge_masses.rows() == profile.edge_imbalances.rows() );
+    assert( profile.edge_masses.cols() == profile.edge_imbalances.cols() );
+    if( profile.edge_masses.rows() <= 1 ) {
+        throw std::runtime_error(
+            "Cannot compute edge correlation of a single sample, as the method is meant to relate "
+            "a set of samples to their meta-data features."
+        );
+    }
 
     LOG_MSG1 << "Calculating correlations and writing files.";
 

src/commands/analyze/dispersion.cpp

@@ -405,6 +405,14 @@ void run_dispersion( DispersionOptions const& options )
 
     // Get the data. Read all samples and calcualte the matrices.
     auto const profile = options.jplace_input.placement_profile();
+    assert( profile.edge_masses.rows() == profile.edge_imbalances.rows() );
+    assert( profile.edge_masses.cols() == profile.edge_imbalances.cols() );
+    if( profile.edge_masses.rows() <= 1 ) {
+        throw std::runtime_error(
+            "Cannot compute edge dispersion of a single sample, as the method is meant to visualize "
+            "dispersion (variance) across a set of samples."
+        );
+    }
 
     LOG_MSG2 << "Calculating dispersions and writing files.";