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POHow use the newton function for root finding of the Scipy's optimize package
 

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  1. POHow use the newton function for root finding of the Scipy's optimize package
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    <p>I want to use the <code>newton</code> function loaded as </p> <pre><code>from scipy.optimize import newton </code></pre> <p>in order to find the zeros of a function enetered by the user. I write a script that first ask to the user to specify a function together with its first derivative, and also the starting point of the algorithm. First of all typing <code>help(newton)</code> I saw which parameters takes the function and the relative explanation: </p> <p><code>newton(func, x0, fprime=None, args=(), tol=1.48e-08, maxiter=50)</code></p> <pre><code>func : function The function whose zero is wanted. It must be a function of a single variable of the form f(x,a,b,c...), where a,b,c... are extra arguments that can be passed in the `args` parameter. </code></pre> <p>In which way I have to pass my function? If I use for func e.g. <code>x**3</code> (and its first derivative) the response is <code>NameError: name 'x' is not defined</code>. On the internet I find that first I have to define my function and its first derivative and pass the names as parameters. So I made the following</p> <pre><code>fie = raw_input('Enter function in terms of x (e.g. x**2 - 2*x). F= ') dfie = raw_input('Enter first derivative of function above DF = ') x0 = input('Enter starting point x0 = ') def F(x,fie): y = eval(fie) return y def DF(x, dfie): dy = eval(dfie) return dy print newton(F,x0,DF) </code></pre> <p>But I get the output </p> <pre><code> 102 for iter in range(maxiter): 103 myargs = (p0,) + args --&gt; 104 fder = fprime(*myargs) 105 if fder == 0: 106 msg = "derivative was zero." TypeError: DF() takes exactly 2 arguments (1 given) </code></pre> <p>and the same issue for <code>F</code> if I omit <code>DF</code>. Looking at the code in <code>/usr/local/share/src/scipy/scipy/optimize/zeros.py</code> I see that it evaluates the first derivative with <code>fder=fprime(*myargs)</code> so maybe I have to put in <code>args</code> something that make it working. I was thinking about it but no solution comes to me. </p>
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    1. USStefano Messina
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