feat:First version of StudentTDistribution.

lib/Statistics/Distributions.rakumod

@@ -15,6 +15,7 @@ constant \ExponentialDistribution is export := Statistics::Distributions::Define
 constant \GammaDistribution is export := Statistics::Distributions::Defined::Gamma;
 constant \MixtureDistribution is export := Statistics::Distributions::Defined::Mixture;
 constant \NormalDistribution is export := Statistics::Distributions::Defined::Normal;
+constant \StudentTDistribution is export := Statistics::Distributions::Defined::StudentT;
 constant \ProductDistribution is export := Statistics::Distributions::Defined::Product;
 constant \UniformDistribution is export := Statistics::Distributions::Defined::Uniform;
 

lib/Statistics/Distributions/Defined.rakumod

@@ -209,6 +209,24 @@ class Product is Generic is export {
 }
 #= Product Distribution objects are created with lists of distribution objects.
 
+#| Student t-distribution class
+class StudentT is Generic is export {
+    has Numeric:D $.nu = 1;
+    #= Degrees of freedom
+    has Numeric:D $.mean = 0;
+    #= Location
+    has Numeric:D $.sd = 1;
+    #= Scale
+    submethod BUILD(:ν(:$!nu) = 1, :µ(:$!mean) = 0, :σ(:$!sd) = 1) {}
+    multi method new($nu) { self.bless(:$nu, mean => 0, sd => 1) }
+    multi method new($nu, $mean, $sd) { self.bless(:$nu, :$mean, :$sd) }
+    multi method generate(UInt:D :$size) {
+        student-t-dist($!nu, $!mean, $!sd, :$size);
+    }
+}
+#= A Student t-distribution object is specified with a positive degrees of freedom parameter (nu), location parameter (mu), and scale parameter (sigma).
+
+
 #| Uniform distribution class
 class Uniform is Generic is export {
     has Numeric:D $.min = 0;

lib/Statistics/Distributions/Utilities.rakumod

@@ -187,7 +187,6 @@ sub product-dist(@dists, UInt:D :$size = 1) is export {
 }
 
 #------------------------------------------------------------
-
 sub chi-squared-dist($nu, UInt:D :$size = 1) is export {
     die "The first argument is expected to be a positive number." unless $nu > 0;
 
@@ -198,4 +197,16 @@ sub chi-squared-dist($nu, UInt:D :$size = 1) is export {
     }
 
     return @variates.List;
+}
+
+#------------------------------------------------------------
+sub student-t-dist($nu, $mean, $sd, Int :$size) is export {
+    my @variates;
+    for ^$size -> $ {
+        my $z = normal-dist(0, 1);
+        my $v = chi-squared-dist($nu).head;
+        my $t = $mean + $sd * ($z / sqrt($v / $nu));
+        @variates.push($t);
+    }
+    return @variates;
 }

t/02-random-variate.rakutest

@@ -125,4 +125,15 @@ subtest {
             'ChiSquareDistribution gives numbers';
 }
 
+# 20
+subtest {
+    ok random-variate(StudentTDistribution.new(ν => 5));
+    ok random-variate(StudentTDistribution.new(ν => 5, μ => 1, σ => 3));
+    dies-ok { random-variate(StudentTDistribution.new(ν => -5)) };
+    isa-ok random-variate(StudentTDistribution.new(3.3)), Numeric:D,
+            'No size argument gives a number for StudentTDistribution';
+    is random-variate(StudentTDistribution.new(20, 1, 3), 10).all ~~ Numeric:D, True,
+            'StudentTDistribution gives numbers with three arguments';
+}
+
 done-testing;