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Runge-Kutta method: Difference between revisions
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Line 85:
y(9.0) = 451.56245928 Error: 4.07232E-05
y(10.0) = 675.99994902 Error: 5.09833E-05</pre>
=={{header|D}}==
{{trans|Ada}}
<lang d>import std.stdio, std.math;
alias real FP;
void runge(in FP function(in FP, in FP) pure nothrow yp_func,
FP[] t, FP[] y, in FP dt) pure nothrow {
foreach (n; 0 .. t.length - 1) {
FP dy1 = dt * yp_func(t[n], y[n]);
FP dy2 = dt * yp_func(t[n] + dt / 2.0, y[n] + dy1 / 2.0);
FP dy3 = dt * yp_func(t[n] + dt / 2.0, y[n] + dy2 / 2.0);
FP dy4 = dt * yp_func(t[n] + dt, y[n] + dy3);
t[n + 1] = t[n] + dt;
y[n + 1] = y[n] + (dy1 + 2.0 * (dy2 + dy3) + dy4) / 6.0;
}
}
FP calc_err(in FP t, in FP calc) pure nothrow {
immutable FP actual = (t ^^ 2 + 4.0) ^^ 2 / 16.0;
return abs(actual - calc);
}
void main() {
enum FP dt = 0.10;
enum size_t N = 101;
FP[N] t_arr, y_arr;
t_arr[0] = 0.0;
y_arr[0] = 1.0;
runge((t, y) => t * sqrt(y), t_arr, y_arr, dt);
foreach (i; 0 .. t_arr.length)
if (i % 10 == 0)
writefln("y(%.1f) = %.8f Error: %.6g",
t_arr[i], y_arr[i],
calc_err(t_arr[i], y_arr[i]));
}</lang>
{{out}}
<pre>y(0.0) = 1.00000000 Error: 0
y(1.0) = 1.56249985 Error: 1.45722e-07
y(2.0) = 3.99999908 Error: 9.19479e-07
y(3.0) = 10.56249709 Error: 2.90956e-06
y(4.0) = 24.99999377 Error: 6.23491e-06
y(5.0) = 52.56248918 Error: 1.08197e-05
y(6.0) = 99.99998341 Error: 1.65946e-05
y(7.0) = 175.56247648 Error: 2.35177e-05
y(8.0) = 288.99996843 Error: 3.15652e-05
y(9.0) = 451.56245928 Error: 4.07232e-05
y(10.0) = 675.99994902 Error: 5.09833e-05</pre>
=={{header|Tcl}}==
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