A number of error messages may be encountered when graphing (apart from messages ingrained in the library functions which I cannot control). Most of them are fatal; the equation cannot be graphed and you must edit it. They will present a popup message box so you know there is a problem.
[Please note that all messages which refer to the variables 'x' or 'y' will actually be 't' or 'r' when you are dealing with a polar equation.]
"Please type an equation in the edit field (or select one from the listbox) first; then press enter or click the Graph button."
You pressed enter on the graph line without selecting or typing in an equation. You need to type in an equation or select one in the list box before you can graph.
"The parser couldn't interpret your equation because of a bad operator or mismatched parentheses. Please edit your equation and try again."
You either left out a paren somewhere, left out one or both of the operands for a binary operation or the argument for a function, or typed some other weird thing the parser and evaluator couldn't digest. Examine your equation carefully and fix whatever seems to be the problem.
"Your equation included a variable or function that Graphmatica does not support, or you mis-typed a function name. Please edit your equation and try again."
Unfortunately, the evaluator isn't set up to return what caused the error, so you'll have to look for it yourself. Check that your equation contains only valid identifiers (see the Operator Table) and that you separated each of them with an operator, space, or some other punctuation.
"The parser couldn't find one of the operands of a binary operation like '+' or the argument to a function you used. Please edit your equation."
The parser couldn't find any identifiers or expressions to use as one of the operands to a binary operation (+, -, *, etc.) or as the argument for a function, like cos(x). All of Graphmatica's functions require one argument following the function name, preferably enclosed in parentheses.
"One or both sides of the equation seems to be blank. Please check that there is an expression on both sides of the equals sign."
Make sure there is some sort of expression on each side of the equation. Obviously, an entry like y= can't produce a meaningful graph.
"No equals sign or more than one found. Press any key to edit equation."
To be a valid and graphable, your equation must include exactly one equals sign [=]. If you get this error, you either left out the = or accidentally typed two or more of them. For parametric equations, there must be an = on each side of the dividing semicolon.
"No dependent variable or more than one 'y' found. Please edit your equation."
Although Graphmatica can isolate ONE 'y' or 'x' variable and graph some relations, it cannot perform the factoring needed to isolate the a variable when both 'x' and 'y' occur more than once. It also cannot plot polar graphs as a function of r instead of t or isolate 'r' when more than one instance is found. If you can adjust the equation so it uses only one instance of the dependent variable, do so; otherwise it can't be graphed. In parametric graphing, this message may also indicate that no 'x' variable was found in the x(t) equation.
"Graphmatica only supports inequalities for single rectangular equations. Please replace the < or > with = and try again."
Inequalities cannot presently be evaluated for polar, parametric, or differential equations. You may still be able to draw the graph if you can express the inequality in rectangular form. Also, the meaning of an inequality operator is ambiguous for an equation containing the "family of functions" parameter a.
"Can't find the inverse of this function of 'y'. Please edit your equation."
You tried to graph an equation like int(y)=x for which y cannot be isolated by taking the inverse of the function. The functions which cannot be isolated are cosh, sinh, tanh, and int. If you can't adjust the equation so this error does not occur, it is not graphable.
"The domain you entered could not be parsed or did not evaluate to one or more constant values. Please edit your equation and try again."
The domain you entered either could not be parsed, or was found to contain a non-constant identifier, like x or y. Valid domains must have at least one side of the range defined and can't contain variables, although any other expression that evaluates to a constant is OK.
"Parametric equation requires that you specify domain! See Parametric Graphing in help file for details."
You typed in a parametric equation (or accidentally hit the semicolon) and neglected to include a closed domain [like {1,6}]. Because the diversity of parametric equations makes it hard to pick a default domain, you have to include one with each parametric graph. [See Parametric Graphing or Specifying a Domain for more help.]
"Not enough initial values supplied to draw graph. Make sure this ODE. includes ## IVs and try again."
Although first-order ODEs may be graphed as a slope-field without providing an initial value, second and higher order equations require that you provide initial values for t, x, dx..., up to the derivative one order less than the highest one in the equation. Make sure that you have specified the right number of valid initial values.
"Drawing flow fields is not supported when using logarithmic graph paper. Change back to linear paper to graph this ODE."
Since it would have required extra work to handle this case, and the meaning of slope on a logarithmic scale is somewhat dubious anyway, I elected not to bother. Please tell me if you have a problem with this.
"Cannot accurately draw the graph of a discontinuous function (like y=w^x, w<0)"
The correct graph of this class of functions has singularities all over the place and thus cannot be drawn accurately using the algorithms Graphmatica normally uses on smooth curves.
"Cannot perform exponential curve fitting on data <= 0."
The exponential equation type fits the linear equation y=ax+b to the logarithms of the data set. Since the logarithm is only defined for values greater than 0, you may not use this curve-fitting technique for data sets that include numbers <= 0.
See also Warning Error Messages