Math & Science ⇒ Wrong Calculations in Function Plot

[computernormal]

Hello forum,

for my bachelor thesis I need to draw the function f(x)=sin(x²).

Code: Select all

\documentclass[11pt]{article}
\usepackage[T1]{fontenc}
\usepackage{pgfplots}

\begin{document}
  \begin{tikzpicture}
    \begin{axis}[
      legend pos=outer north east,
      grid=major,
      xlabel=$t$,
      ylabel=$f(t)$,
      xmin=0
    ]
      \addplot [smooth, blue, mark=none]{sin(deg(x^2))};
      \legend{$f(t)=\sin(x^2)$};
    \end{axis}
  \end{tikzpicture}
\end{document}

But this code shows me the following function.

plot-sine-squared.png (9.25 KiB) Viewed 5281 times

In a calculation table by tabularcalc or in other online function drawers is the function value for f(4,8)=-0.88!

Code: Select all

\documentclass[11pt]{article}
\usepackage[T1]{fontenc}
\usepackage{tabularcalc}

\begin{document}
  \htablecalc[3]{$x$}{x=4.8}
    {$f(x)=x$}{x}
    {$g(x)=x^{2}$}{sin(deg(x^2))}
    {$h(x)=\sqrt{x^{2}}$}{round(root(2,x*x),3)}
\end{document}

The result is this.

table-sine-squared.png (5.72 KiB) Viewed 5281 times

Why does LaTeX draw false here?

Greetings
Andre

[mas]

I have not used tabularcalc. But it looks like the problem seems to be in the units used.

sin(4.8**2) (for radians) will give you -0.88. sin(4.8**2) (for degrees) is 0.39137.

You are plotting the graph using degrees. Try using a single unit.

[cgnieder]

The function is correct (http://www.wolframalpha.com/input/?i=sin%28x^2%29) and the plot nearly: you need a higher sampling:

Code: Select all

\documentclass{article}
\usepackage{pgfplots}

\begin{document}
  \begin{tikzpicture}
    \begin{axis}[
      legend pos=outer north east,
      grid=major,
      xlabel=$t$,
      ylabel=$f(t)$,
      xmin=0
    ]
      \addplot[smooth, blue, mark=none,samples=200]{sin(deg(x^2))};
      \legend{$f(t)=\sin(x^2)$};
    \end{axis}
  \end{tikzpicture}
\end{document}

Regards

[computernormal]

Thanks ... saved my day