File:TrivFctRootExm.pdf

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English: The function g: RR is a trivial 5th functional root of f: R+R+ defined by f(x) = sin(x). The computation of f(π/6) = 1/2 = g5(π/6) is shown. See File:TrivFctRootDef.pdf for the definition of g, given an arbitrary f: R+R+ and nN, and the computation of gn(x) = f(x) for all xR+.
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Source Own work
Author Jochen Burghardt
Other versions File:TrivFctRootExm.pdf * File:TrivFctRootExm svg.svg * File:TrivFctRootDef.pdf
C source code for example coordinates
#include <stdio.h>
#include <math.h>

static int const n = 5;
static double f(double x) { return sin(x); }

static double g(double x) {
    if (0.0           <= x                     )   return atan(x) - M_PI;
    if (-(n-1)*M_PI/2 <= x && x < 0            )   return x - M_PI/2;
    if (-n*M_PI/2     <= x && x < -(n-1)*M_PI/2)   return f(tan(x+n*M_PI/2));
    return 0.0;
}

int main(void) {
    int i;
    double gi; 
    while (1) {
        printf("enter:\n");
        scanf(" %lf",&gi);
        for (i=0; i<=n; ++i) {
            printf("g^%d(x) = %f\n",i,gi);
            gi = g(gi);
        }
    }   
    return 0;
}
Gnuplot source code
# given:
n = 5 
f(x) = sin(x)

# trivial function root:
g(x) =  ( 0 <= x                          ? atan(x) - pi                \
        : -(n-1)*pi/2 <= x && x < 0       ? x - pi/2            \
        : -n*pi/2 <= x && x < -(n-1)*pi/2 ? f(tan(x+n*pi/2))    \   
        :                                   0                   \
        )

xmin = -8
xmax = 7 
ymin = -8
ymax = 2 

set xrange[xmin:xmax]
set yrange[ymin:ymax]
set grid
set xtics pi/2
set ytics pi/2
set format x "%5.2f"
set format y "%5.2f"
set key right bottom

# coordinate cross:
set arrow from xmin , 0    to xmax , 0    nohead lt 8
set arrow from 0    , ymin to 0    , ymax nohead lt 8

# shift ranges:
set arrow from -1*pi/2 , ymin to -1*pi/2 , ymax nohead lt 5
set arrow from -2*pi/2 , ymin to -2*pi/2 , ymax nohead lt 5
set arrow from -3*pi/2 , ymin to -3*pi/2 , ymax nohead lt 5
set arrow from -4*pi/2 , ymin to -4*pi/2 , ymax nohead lt 5
set arrow from -5*pi/2 , ymin to -5*pi/2 , ymax nohead lc 5

# 1 input/output example f:
set arrow from 0.523599 , 0 to 0.523599 , 0.500000 lt 1

# 5 input/output examples g:
set arrow from  0.523599 , 0         to  0.523599 , -2.659245 lt 2
set arrow from  0.523599 , -2.659245 to -2.659245 , -2.659245 lt 2
set arrow from -2.659245 , -2.659245 to -2.659245 , -4.230041 lt 2
set arrow from -2.659245 , -4.230041 to -4.230041 , -4.230041 lt 2
set arrow from -4.230041 , -4.230041 to -4.230041 , -5.800837 lt 2
set arrow from -4.230041 , -5.800837 to -5.800837 , -5.800837 lt 2
set arrow from -5.800837 , -5.800837 to -5.800837 , -7.371634 lt 2
set arrow from -5.800837 , -7.371634 to -7.371634 , -7.371634 lt 2
set arrow from -7.371634 , -7.371634 to -7.371634 ,  0.500000 lt 2

  plot            x    with lines       lt 7
replot [x=0:xmax] f(x) with lines  lw 3 lt 1 title"f(x)"
replot            g(x) with lines  lw 3 lt 2
pause -1

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I, the copyright holder of this work, hereby publish it under the following license:
w:en:Creative Commons
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You are free:
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Under the following conditions:
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File history

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Date/TimeThumbnailDimensionsUserComment
current09:14, 6 August 2020Thumbnail for version as of 09:14, 6 August 20203,087 × 2,045 (11 KB)Jochen Burghardt (talk | contribs)exchange role for f and g to fit with article naming
08:58, 6 August 2020No thumbnail0 × 0 (11 KB)Jochen Burghardt (talk | contribs)show g: R+ --> R rather than g: R --> R
07:40, 6 August 2020No thumbnail0 × 0 (11 KB)Jochen Burghardt (talk | contribs)Uploaded own work with UploadWizard

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