diff --git a/main/ejml-simple/src/org/ejml/simple/AutomaticSimpleMatrixConvert.java b/main/ejml-simple/src/org/ejml/simple/AutomaticSimpleMatrixConvert.java
index 93c933e6..5cc16a3c 100644
--- a/main/ejml-simple/src/org/ejml/simple/AutomaticSimpleMatrixConvert.java
+++ b/main/ejml-simple/src/org/ejml/simple/AutomaticSimpleMatrixConvert.java
@@ -30,20 +30,20 @@
 public class AutomaticSimpleMatrixConvert {
     MatrixType commonType;
 
-    public void specify0( SimpleBase a, SimpleBase... inputs ) {
-        SimpleBase array[] = new SimpleBase[inputs.length + 1];
+    public void specify0( ConstMatrix<?> a, ConstMatrix<?>... inputs ) {
+        var array = new ConstMatrix[inputs.length + 1];
         System.arraycopy(inputs, 0, array, 0, inputs.length);
         array[inputs.length] = a;
         specify(array);
     }
 
-    public void specify( SimpleBase... inputs ) {
+    public void specify( ConstMatrix<?>... inputs ) {
         boolean dense = false;
         boolean real = true;
         int bits = 32;
 
-        for (SimpleBase s : inputs) {
-            MatrixType t = s.mat.getType();
+        for (ConstMatrix<?> s : inputs) {
+            MatrixType t = s.getType();
             if (t.isDense())
                 dense = true;
             if (!t.isReal())
@@ -55,7 +55,7 @@ public void specify( SimpleBase... inputs ) {
         commonType = MatrixType.lookup(dense, real, bits);
     }
 
-    public <T extends SimpleBase<T>> T convert( SimpleBase matrix ) {
+    public <T extends SimpleBase<T>> T convert( SimpleBase<?> matrix ) {
         if (matrix.getType() == commonType)
             return (T)matrix;
 
diff --git a/main/ejml-simple/src/org/ejml/simple/ConstMatrix.java b/main/ejml-simple/src/org/ejml/simple/ConstMatrix.java
index f704e082..7eb155fe 100644
--- a/main/ejml-simple/src/org/ejml/simple/ConstMatrix.java
+++ b/main/ejml-simple/src/org/ejml/simple/ConstMatrix.java
@@ -36,6 +36,9 @@
  * local copy that can't be accessed externally.
  * </p>
  *
+ * <p>NOTE: Implementations of ConstMatrix must extend {@link SimpleBase} or else it won't work when given as
+ * input to any class based off of {@link SimpleBase}.</p>
+ *
  * @author Peter Abeles
  */
 public interface ConstMatrix<T extends ConstMatrix<T>> {
@@ -65,7 +68,7 @@ public interface ConstMatrix<T extends ConstMatrix<T>> {
      * where c is the returned matrix, a is this matrix, and b is the passed in matrix.
      * </p>
      *
-     * @param B A matrix that is n by bn. Not modified.
+     * @param B A matrix that is n by p. Not modified.
      * @return The results of this operation.
      * @see CommonOps_DDRM#mult(DMatrix1Row, DMatrix1Row, DMatrix1Row)
      */
@@ -98,7 +101,6 @@ public interface ConstMatrix<T extends ConstMatrix<T>> {
      */
     T plus( ConstMatrix<?> B );
 
-
     /**
      * <p>
      * Returns the result of matrix subtraction:<br>
@@ -141,7 +143,6 @@ public interface ConstMatrix<T extends ConstMatrix<T>> {
      */
     T minusComplex( double real, double imag );
 
-
     /**
      * <p>
      * Returns the result of scalar addition:<br>
@@ -767,6 +768,28 @@ default int getNumElements() {
      */
     T cols( int begin, int end );
 
+    /**
+     * <p>Concatenates all the matrices together along their columns. If the rows do not match the upper elements
+     * are set to zero.</p>
+     *
+     * A = [ this, m[0] , ... , m[n-1] ]
+     *
+     * @param matrices Set of matrices
+     * @return Resulting matrix
+     */
+    T concatColumns( ConstMatrix<?>... matrices );
+
+    /**
+     * <p>Concatenates all the matrices together along their columns. If the rows do not match the upper elements
+     * are set to zero.</p>
+     *
+     * A = [ this; m[0] ; ... ; m[n-1] ]
+     *
+     * @param matrices Set of matrices
+     * @return Resulting matrix
+     */
+    T concatRows( ConstMatrix<?>... matrices );
+
     /**
      * Returns the type of matrix it is wrapping.
      */
diff --git a/main/ejml-simple/src/org/ejml/simple/SimpleBase.java b/main/ejml-simple/src/org/ejml/simple/SimpleBase.java
index f855442d..ec712bfd 100644
--- a/main/ejml-simple/src/org/ejml/simple/SimpleBase.java
+++ b/main/ejml-simple/src/org/ejml/simple/SimpleBase.java
@@ -211,7 +211,7 @@ protected static SimpleOperations lookupOps( MatrixType type ) {
     }
 
     /** {@inheritDoc} */
-    @Override public T plus( ConstMatrix _B ) {
+    @Override public T plus( ConstMatrix<?> _B ) {
         T B = (T)_B;
         convertType.specify(this, B);
         T A = convertType.convert(this);
@@ -279,7 +279,7 @@ protected static SimpleOperations lookupOps( MatrixType type ) {
     }
 
     /** {@inheritDoc} */
-    @Override public T plus( double beta, ConstMatrix _B ) {
+    @Override public T plus( double beta, ConstMatrix<?> _B ) {
         T B = (T)_B;
         convertType.specify(this, B);
         T A = convertType.convert(this);
@@ -291,7 +291,7 @@ protected static SimpleOperations lookupOps( MatrixType type ) {
     }
 
     /** {@inheritDoc} */
-    @Override public double dot( ConstMatrix _v ) {
+    @Override public double dot( ConstMatrix<?> _v ) {
         T v = (T)_v;
         convertType.specify(this, v);
         T A = convertType.convert(this);
@@ -581,7 +581,7 @@ public void setRow( int row, int startColumn, double... values ) {
      * @param row Row in 'this'
      * @param src Vector which is to be copied into the row
      */
-    public void setRow( int row, SimpleMatrix src ) {
+    public void setRow( int row, ConstMatrix<?> src ) {
         if (!src.isVector())
             throw new IllegalArgumentException("Input matrix must be a vector");
         if (src.getNumElements() != numCols())
@@ -596,9 +596,10 @@ public void setRow( int row, SimpleMatrix src ) {
         }
 
         // See if it's a row or column vector and grab the appropriate elements.
-        double[] vector = src.numRows() < src.numCols() ?
-                src.ops.getRow(src.mat, 0, 0, src.getNumElements()) :
-                src.ops.getColumn(src.mat, 0, 0, src.getNumElements());
+        var bsrc = (SimpleBase)src;
+        double[] vector = src.getNumRows() < src.getNumCols() ?
+                bsrc.ops.getRow(bsrc.mat, 0, 0, src.getNumElements()) :
+                bsrc.ops.getColumn(bsrc.mat, 0, 0, src.getNumElements());
 
         // If src is real but output is complex, convert the vector.
         if (src.getType().isReal() && !getType().isReal()) {
@@ -631,7 +632,7 @@ public void setColumn( int column, int startRow, double... values ) {
      * @param column Column in 'this'
      * @param src Vector which is to be copied into the column
      */
-    public void setColumn( int column, SimpleMatrix src ) {
+    public void setColumn( int column, ConstMatrix<?> src ) {
         if (!src.isVector())
             throw new IllegalArgumentException("Input matrix must be a vector");
         if (src.getNumElements() != numRows())
@@ -646,9 +647,10 @@ public void setColumn( int column, SimpleMatrix src ) {
         }
 
         // See if it's a row or column vector and grab the appropriate elements.
-        double[] vector = src.numRows() < src.numCols() ?
-                src.ops.getRow(src.mat, 0, 0, src.getNumElements()) :
-                src.ops.getColumn(src.mat, 0, 0, src.getNumElements());
+        var bsrc = (SimpleBase)src;
+        double[] vector = src.getNumRows() < src.getNumCols() ?
+                bsrc.ops.getRow(bsrc.mat, 0, 0, src.getNumElements()) :
+                bsrc.ops.getColumn(bsrc.mat, 0, 0, src.getNumElements());
 
         // If src is real but output is complex, convert the vector.
         if (src.getType().isReal() && !getType().isReal()) {
@@ -1217,24 +1219,16 @@ public void printDimensions() {
         return mat.getType().getBits();
     }
 
-    /**
-     * <p>Concatenates all the matrices together along their columns. If the rows do not match the upper elements
-     * are set to zero.</p>
-     *
-     * A = [ this, m[0] , ... , m[n-1] ]
-     *
-     * @param matrices Set of matrices
-     * @return Resulting matrix
-     */
-    public T concatColumns( SimpleBase<?>... matrices ) {
+    /** {@inheritDoc} */
+    @Override public T concatColumns( ConstMatrix<?>... matrices ) {
         convertType.specify0(this, matrices);
         T A = convertType.convert(this);
 
         int numCols = A.numCols();
         int numRows = A.numRows();
         for (int i = 0; i < matrices.length; i++) {
-            numRows = Math.max(numRows, matrices[i].numRows());
-            numCols += matrices[i].numCols();
+            numRows = Math.max(numRows, matrices[i].getNumRows());
+            numCols += matrices[i].getNumCols();
         }
 
         SimpleMatrix combined = SimpleMatrix.wrap(convertType.commonType.create(numRows, numCols));
@@ -1242,7 +1236,7 @@ public T concatColumns( SimpleBase<?>... matrices ) {
         A.ops.extract(A.mat, 0, A.numRows(), 0, A.numCols(), combined.mat, 0, 0);
         int col = A.numCols();
         for (int i = 0; i < matrices.length; i++) {
-            Matrix m = convertType.convert(matrices[i]).mat;
+            Matrix m = convertType.convert((SimpleBase)matrices[i]).mat;
             int cols = m.getNumCols();
             int rows = m.getNumRows();
             A.ops.extract(m, 0, rows, 0, cols, combined.mat, 0, col);
@@ -1252,24 +1246,16 @@ public T concatColumns( SimpleBase<?>... matrices ) {
         return (T)combined;
     }
 
-    /**
-     * <p>Concatenates all the matrices together along their columns. If the rows do not match the upper elements
-     * are set to zero.</p>
-     *
-     * A = [ this; m[0] ; ... ; m[n-1] ]
-     *
-     * @param matrices Set of matrices
-     * @return Resulting matrix
-     */
-    public T concatRows( SimpleBase<?>... matrices ) {
+    /** {@inheritDoc} */
+    @Override public T concatRows( ConstMatrix<?>... matrices ) {
         convertType.specify0(this, matrices);
         T A = convertType.convert(this);
 
         int numCols = A.numCols();
         int numRows = A.numRows();
         for (int i = 0; i < matrices.length; i++) {
-            numRows += matrices[i].numRows();
-            numCols = Math.max(numCols, matrices[i].numCols());
+            numRows += matrices[i].getNumRows();
+            numCols = Math.max(numCols, matrices[i].getNumCols());
         }
 
         SimpleMatrix combined = SimpleMatrix.wrap(convertType.commonType.create(numRows, numCols));
@@ -1277,7 +1263,7 @@ public T concatRows( SimpleBase<?>... matrices ) {
         A.ops.extract(A.mat, 0, A.numRows(), 0, A.numCols(), combined.mat, 0, 0);
         int row = A.numRows();
         for (int i = 0; i < matrices.length; i++) {
-            Matrix m = convertType.convert(matrices[i]).mat;
+            Matrix m = convertType.convert((SimpleBase)matrices[i]).mat;
             int cols = m.getNumCols();
             int rows = m.getNumRows();
             A.ops.extract(m, 0, rows, 0, cols, combined.mat, row, 0);