September Morn Update

Task/Multiple-regression/Phix/multiple-regression.phix

@@ -0,0 +1,54 @@
+constant N = 15, M=3
+sequence x = {1.47,1.50,1.52,1.55,1.57,
+              1.60,1.63,1.65,1.68,1.70,
+              1.73,1.75,1.78,1.80,1.83},
+         y = {52.21,53.12,54.48,55.84,57.20,
+              58.57,59.93,61.29,63.11,64.47,
+              66.28,68.10,69.92,72.19,74.46},
+         s = repeat(0,N),
+         t = repeat(0,N),
+         a = repeat(repeat(0,M+1),M)
+
+    for k=1 to 2*M do
+        for i=1 to N do
+            s[k] += power(x[i],k-1)
+            if k<=M then t[k] += y[i]*power(x[i],k-1) end if
+        end for
+    end for
+
+    -- build linear system
+
+    for row=1 to M do
+        for col=1 to M do
+            a[row,col] = s[row+col-1]
+        end for
+        a[row,M+1] = t[row]
+    end for
+
+    puts(1,"Linear system coefficents:\n")
+    pp(a,{pp_Nest,1,pp_IntFmt,"%7.1f",pp_FltFmt,"%7.1f"})
+
+    for j=1 to M do
+        integer i = j
+        while a[i,j]=0 do i += 1 end while
+        if i=M+1 then
+            ?"SINGULAR MATRIX !"
+            ?9/0
+        end if
+        for k=1 to M+1 do
+            {a[j,k],a[i,k]} = {a[i,k],a[j,k]}
+        end for
+        atom Y = 1/a[j,j]
+        a[j] = sq_mul(a[j],Y)
+        for i=1 to M do
+            if i<>j then
+                Y=-a[i,j]
+                for k=1 to M+1 do
+                    a[i,k] += Y*a[j,k]
+                end for
+            end if
+        end for
+    end for
+
+    puts(1,"Solutions:\n")
+    ?columnize(a,M+1)[1]