Troubleshooting:Common Mistakes

From MathLab

Contents 1 Mathematica Reference Page 1.1 Common Mistakes 1.2 Avoiding Common Mistakes 1.3 Error Messages 1.4 Printing Problems

[edit] Mathematica Reference Page

[edit] Common Mistakes

Most Mathematica syntax problems are of a very few types: (Green denote proper Mathematica syntax, red expressions result in errors.)

1. Parenthesis (), Braces {}, and Brackets [].
   • Parenthesis are for breaking up multiplication and addition e.g. (x+2)^2 is the same as x^2 + 4 x + 4.
   • Braces {} are for grouping things together e.g. {1, 2} is the point or vector with coordinates x=1, and y=2.
   • Brackets [] are for functions e.g. Sin[x].
2. Capitalization. All Mathematica commands start with a Capital letter.
   • Sin[x] not sin[x].
   • Plot[Cos[x],{x,0,4}] not plot[Cos[x],{x,0,4}]
   • Pi or the pretty version on the Pallete not pi
   • E or the pretty version on the Pallete not e
   • etc.
3. Missing commas.
   • Plot[Cos[x],{x,0,4}] not Plot[Cos[x]{x,0,4}]
4. Bad function definitions.

   f[x_] = Cos[x^2] defines a function. Common mistakes are:

   • f[x] = Cos[x^2]

     missing underscore.

   • f(x_) = Cos[x^2]

     It needs brackets [] not parens ().

5. Printing without using Mathematica fonts.
   • This will cause weird characters to print all over the page.

examples of the error messages priduced by these errors are below.

[edit] Avoiding Common Mistakes

Avoiding these mistakes is simple:

1. Parenthesis (), Braces {}, and Brackets []. Remeber the rules:
   • Parenthesis () are for breaking up multiplication and addition
   • Braces {} are for grouping things together
   • Brackets [] are for functions
   • Capitalization. Remember ll Mathematica commands start with a Capital letter.
   • Paste from the Palette.
   • Always Capitalize
2. Missing commas.
   • Paste from the palette and fill in the template.
   • Copy carefully from the Help.
3. Bad function definitions.
   • Remember the underscore.
   • Remember to use brackets [].
4. Printing without using Mathematica fonts.
   • Put a checkmark in the box next to 'Print using Mathematica fonts'.

     This will prevent weird characters on your printed labs.

[edit] Error Messages

These syntax errors produce (once you know how to read them) fairly clear (well compared to Matlab, Maple, Fortran, C++, Java, etc.) error messages. the trick is to only look at the first message.

1. Parenthesis (), Braces {}, and Brackets [].
   • Plot[Sin(x),{x,0,4}]

     produces the error message

     sin x is not a real number at x=1.66666 x 10^-7

     In other words it thinks sin and x are two seperate things.

   • Plot(Sin[x],{x,0,4})

     produces the message "(" can not be followed by "Sin[x], {x,0,4})".

   • Expand[ (x+2)^2] gives x^2 + 4 x + 4
   • What do you think

     Plot[ {Sin[x], Cos[x]},{x, 0, Pi}]

     will give? Remember the braces group things together.

2. Capitalization. All Mathematica commands start with a Capital letter.
   • Plot[sin[x],{x,0,4}]

     produces the error message

     sin(x) is not a real number at x=1.66666 x 10^-7

     In other words it does not understand sin[x].

   • plot[Cos[x],{x,0,4}]

     Just parrots back the command. This is what Mathematica does when it does not know what to do. You also get a warning the first time you do this that "plot" is similar to "Plot".

   • Plot[ Cos[x],{x,0,pi}]

     gives the message that

     Limiting value pi in {x,0,pi} is not a real number.

   • Plot[e^x, {x, 0, Pi}]

     gives the message that e^x is not a real number at x=1.309 x 10^(-7).

3. Missing commas.
   • Plot[Cos[x]{x,0,4}]

     produces the message

     Plot called with one argument; 2 or more arguments are expected.

4. Bad function definitions.
   • After defining f[x_] = Cos[x^2]

     f'[x] gives the derivative -2 x Sin[x^2].

   • After running f[x] = Cos[x^2]

     f'[x] simply parrots.

   • f(x_) = Cos[x^2]

     produces the strange message

     Tag Times in ..... is protected.

[edit] Printing Problems

If you get strange characters printed throughout your printed lab, make sure you have the "Print With Mathematica Fonts" option selected (button depressed).