Minor changes to Permutation class.

Add overloads for Invert() and IsValid() methods taking the permutation length as argument.

Author: wo80

CSparse/CSparse.csproj

@@ -1,32 +1,39 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
     <GeneratePackageOnBuild>False</GeneratePackageOnBuild>
-    <GenerateDocumentationFile>true</GenerateDocumentationFile>
+    <GenerateDocumentationFile>True</GenerateDocumentationFile>
     <PackageId>CSparse</PackageId>
     <Summary>A concise library for solving sparse linear systems with direct methods.</Summary>
     <Description>CSparse.NET provides numerical methods for sparse LU, Cholesky and QR decomposition of real and complex linear systems.</Description>
     <Product>CSparse.NET</Product>
     <Company />
-    <Copyright>Copyright Christian Woltering © 2012-2022</Copyright>
+    <Copyright>Copyright Christian Woltering © 2012-2023</Copyright>
     <Authors>Christian Woltering</Authors>
-    <AssemblyVersion>3.7.0.0</AssemblyVersion>
-    <FileVersion>3.7.0.0</FileVersion>
+    <AssemblyVersion>3.8.1.0</AssemblyVersion>
+    <FileVersion>3.8.1.0</FileVersion>
     <PackageTags>math sparse matrix lu cholesky qr decomposition factorization </PackageTags>
-    <Version>3.7.0</Version>
+    <Version>3.8.1</Version>
     <AssemblyName>CSparse</AssemblyName>
     <RootNamespace>CSparse</RootNamespace>
     <PackageLicenseExpression>LGPL-2.1-only</PackageLicenseExpression>
     <PackageProjectUrl>https://github.com/wo80/CSparse.NET</PackageProjectUrl>
     <RepositoryUrl>https://github.com/wo80/CSparse.NET</RepositoryUrl>
     <RepositoryType>git</RepositoryType>
-    <PackageReleaseNotes>Add sparse matrix OfDiagonals static method (similar to MATLAB spdiags).
-</PackageReleaseNotes>
+    <PackageReleaseNotes>
+Changes in version 3.8.1:
+
+* Add overloads for permutation Invert() and IsValid() methods taking the permutation length as argument.
+
+Changes in version 3.8.0:
+
+* Add overloads for the factorization Solve() methods taking Span&lt;T&gt; as argument. Note that this introduces a dependency on System.Memory for the netstandard2.0 assembly.
+    </PackageReleaseNotes>
   </PropertyGroup>
 
   <ItemGroup>
-      <PackageReference Include="System.Memory" Version="4.5.5" Condition="'$(TargetFramework)' == 'netstandard2.0'"/>
+    <PackageReference Include="System.Memory" Version="4.5.5" Condition="'$(TargetFramework)' == 'netstandard2.0'"/>
   </ItemGroup>
 
   <ItemGroup>

CSparse/Permutation.cs

@@ -142,11 +142,20 @@ public static int[] Create(int n, int seed = 0)
         /// <returns>Returns pinv[i] = k if p[k] = i on input.</returns>
         public static int[] Invert(int[] p)
         {
-            int k, n = p.Length;
+            return Invert(p, p.Length);
+        }
 
+        /// <summary>
+        /// Inverts a permutation vector.
+        /// </summary>
+        /// <param name="p">A permutation vector.</param>
+        /// <param name="n">Length of the permutation.</param>
+        /// <returns>Returns pinv[i] = k if p[k] = i on input.</returns>
+        public static int[] Invert(int[] p, int n)
+        {
             int[] pinv = new int[n];
 
-            for (k = 0; k < n; k++)
+            for (int k = 0; k < n; k++)
             {
                 // Invert the permutation.
                 pinv[p[k]] = k;
@@ -162,21 +171,31 @@ public static int[] Invert(int[] p)
         /// <returns>True if <paramref name="p"/> represents a proper permutation, <c>false</c> otherwise.</returns>
         public static bool IsValid(int[] p)
         {
-            int length = p.Length;
+            return IsValid(p, p.Length);
+        }
 
-            var check = new bool[length];
+        /// <summary>
+        /// Checks whether the <paramref name="p"/> array represents a proper permutation.
+        /// </summary>
+        /// <param name="p">An array which represents where each integer is permuted too: indices[i]
+        /// represents that integer i is permuted to location indices[i].</param>
+        /// <param name="n">Length of the permutation.</param>
+        /// <returns>True if <paramref name="p"/> represents a proper permutation, <c>false</c> otherwise.</returns>
+        public static bool IsValid(int[] p, int n)
+        {
+            var check = new bool[n];
 
-            for (int i = 0; i < length; i++)
+            for (int i = 0; i < n; i++)
             {
-                if (p[i] >= length || p[i] < 0)
+                if (p[i] >= n || p[i] < 0)
                 {
                     return false;
                 }
 
                 check[p[i]] = true;
             }
 
-            for (int i = 0; i < length; i++)
+            for (int i = 0; i < n; i++)
             {
                 if (check[i] == false)
                 {