Changeset 996Tweet

Timestamp:

Sep 28, 2011, 7:05:00 PM (11 years ago)

Author:

sam

Message:

test: minor updates to the Pi program (now almost deprecated) and the
Remez exchange program.

Location:

trunk/test/math

Files:

• pi.cpp (modified) (1 diff)
• remez.cpp (modified) (6 diffs)

trunk/test/math/pi.cpp

@@ -19 +19 @@
 int main(int argc, char **argv)
 {
-    /* Approximate Pi using Machin's formula: 16*atan(1/5)-4*atan(1/239) */
-    real sum = 0.0, x0 = 5.0, x1 = 239.0;
-    real const m0 = -x0 * x0, m1 = -x1 * x1, r16 = 16.0, r4 = 4.0;
+    printf("Pi: "); real::R_PI.print();
+    printf("e: "); real::R_E.print();
+    printf("ln(2): "); real::R_LN2.print();
+    printf("sqrt(2): "); real::R_SQRT2.print();
+    printf("sqrt(1/2): "); real::R_SQRT1_2.print();
 
-    /* Degree 240 is required for 512-bit mantissa precision */
-    for (int i = 1; i < 240; i += 2)
+    /* Gauss-Legendre computation of Pi -- doesn't work well at all,
+     * probably because we use finite precision. */
+    real a = 1.0, b = sqrt((real)0.5), t = 0.25, p = 1.0;
+
+    for (int i = 0; i < 3; i++)
     {
-        sum += r16 / (x0 * (real)i) - r4 / (x1 * (real)i);
-        x0 *= m0;
-        x1 *= m1;
+        real a2 = (a + b) * (real)0.5;
+        real b2 = sqrt(a * b);
+        real tmp = a - a2;
+        real t2 = t - p * tmp * tmp;
+        real p2 = p + p;
+        a = a2; b = b2; t = t2; p = p2;
     }
 
-    sum.print();
-
-    /* Bonus: compute e for fun. */
-    sum = 0.0;
-    x0 = 1.0;
-
-    for (int i = 1; i < 100; i++)
-    {
-        sum += fres(x0);
-        x0 *= (real)i;
-    }
-
+    real sum = a + b;
+    sum = sum * sum / ((real)4 * t);
     sum.print();
 

trunk/test/math/remez.cpp

@@ -20 +20 @@
 
 /* The order of the approximation we're looking for */
-static int const ORDER = 4;
+static int const ORDER = 8;
+
+static real compute_pi()
+{
+    /* Approximate Pi using Machin's formula: 16*atan(1/5)-4*atan(1/239) */
+    real sum = 0.0, x0 = 5.0, x1 = 239.0;
+    real const m0 = -x0 * x0, m1 = -x1 * x1, r16 = 16.0, r4 = 4.0;
+
+    /* Degree 240 is required for 512-bit mantissa precision */
+    for (int i = 1; i < 240; i += 2)
+    {
+        sum += r16 / (x0 * (real)i) - r4 / (x1 * (real)i);
+        x0 *= m0;
+        x1 *= m1;
+    }
+    return sum;
+}
 
 /* The function we want to approximate */
-real myfun(real const &x)
-{
+static real myfun(real const &x)
+{
+    static real const half_pi = compute_pi() * (real)0.5;
     static real const one = 1.0;
-    return cos(x) - one;
+    if (x == (real)0.0 || x == (real)-0.0)
+        return half_pi;
+    return sin(x * half_pi) / x;
+    //return cos(x) - one;
     //return exp(x);
 }
@@ -47 +67 @@
     Matrix<N> inv() const
     {
-        Matrix a = *this, b(real(1.0));
+        Matrix a = *this, b((real)1.0);
 
         /* Inversion method: iterate through all columns and make sure
@@ -73 +93 @@
             /* Now we know the diagonal term is non-zero. Get its inverse
              * and use that to nullify all other terms in the column */
-            real x = fres(a.m[i][i]);
+            real x = (real)1.0 / a.m[i][i];
             for (int j = 0; j < N; j++)
             {
@@ -163 +183 @@
     for (int i = 0; i < ORDER + 1; i++)
     {
-        zeroes[i] = real(2 * i - ORDER) / real(ORDER + 1);
+        zeroes[i] = (real)(2 * i - ORDER) / (real)(ORDER + 1);
         fxn[i] = myfun(zeroes[i]);
     }
@@ -184 +204 @@
             for (int k = 0; k < ORDER + 1; k++)
                 if (cheby[n][k])
-                    sum += real(cheby[n][k]) * powers[k];
+                    sum += (real)cheby[n][k] * powers[k];
             mat.m[i][n] = sum;
         }
@@ -308 +328 @@
             for (int k = 0; k < ORDER + 1; k++)
                 if (cheby[n][k])
-                    sum += real(cheby[n][k]) * powers[k];
+                    sum += (real)cheby[n][k] * powers[k];
             mat.m[i][n] = sum;
         }