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<title>Quadratic Equations - GNU Scientific Library -- Reference Manual</title>
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<h3 class="section">6.3 Quadratic Equations</h3>
<p><a name="index-quadratic-equation_002c-solving-228"></a>
<div class="defun">
— Function: int <b>gsl_poly_solve_quadratic</b> (<var>double a, double b, double c, double * x0, double * x1</var>)<var><a name="index-gsl_005fpoly_005fsolve_005fquadratic-229"></a></var><br>
<blockquote><p>This function finds the real roots of the quadratic equation,
<pre class="example"> a x^2 + b x + c = 0
</pre>
<p class="noindent">The number of real roots (either zero, one or two) is returned, and
their locations are stored in <var>x0</var> and <var>x1</var>. If no real roots
are found then <var>x0</var> and <var>x1</var> are not modified. If one real root
is found (i.e. if a=0) then it is stored in <var>x0</var>. When two
real roots are found they are stored in <var>x0</var> and <var>x1</var> in
ascending order. The case of coincident roots is not considered
special. For example (x-1)^2=0 will have two roots, which happen
to have exactly equal values.
<p>The number of roots found depends on the sign of the discriminant
b^2 - 4 a c. This will be subject to rounding and cancellation
errors when computed in double precision, and will also be subject to
errors if the coefficients of the polynomial are inexact. These errors
may cause a discrete change in the number of roots. However, for
polynomials with small integer coefficients the discriminant can always
be computed exactly.
</blockquote></div>
<div class="defun">
— Function: int <b>gsl_poly_complex_solve_quadratic</b> (<var>double a, double b, double c, gsl_complex * z0, gsl_complex * z1</var>)<var><a name="index-gsl_005fpoly_005fcomplex_005fsolve_005fquadratic-230"></a></var><br>
<blockquote>
<p>This function finds the complex roots of the quadratic equation,
<pre class="example"> a z^2 + b z + c = 0
</pre>
<p class="noindent">The number of complex roots is returned (either one or two) and the
locations of the roots are stored in <var>z0</var> and <var>z1</var>. The roots
are returned in ascending order, sorted first by their real components
and then by their imaginary components. If only one real root is found
(i.e. if a=0) then it is stored in <var>z0</var>.
</blockquote></div>
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