An example in Manipulating Expressions in Programming Methods, showed how to use the Substitute Into() function to input coefficients for a quadratic polynomial into the quadratic formula and then use the formula to calculate the roots of the polynomial. That example required specifying the coefficients as arguments to Substitute Into().
The section Construct a Column Dialog shows an example to collect coefficients from the user using a modal dialog box.
myCoeffs = New Window( "Find the roots for the equation",
// create a window to collect coefficients from the user
<<Modal,
H List Box(
a = Number Edit Box( 1 ),
Text Box( "*x^2 + " ),
b = Number Edit Box( 2 ),
Text Box( "*x + " ),
c = Number Edit Box( 1 ),
Text Box( " = 0" )
),
Button Box( "OK",
a = a << Get;
b = b << Get;
c = c << Get;
Show( a, b, c );
),
Button Box( "Cancel" )
);
x = {Expr(
(-b + Sqrt( b ^ 2 - 4 * a * c )) / (2 * a)
), Expr(
(-b - Sqrt( b ^ 2 - 4 * a * c )) / (2 * a)
)};
/* calculate the results: The quadratic formula is
x=(-b + - sqrt(b^2 - 4ac))/2a. Plug the coefficients into
the quadratic formula */
xx = Eval Expr( x );
// store the solution list
results = Expr(
/* test whether real roots were found and make an appropriate display
if yes (for example, with the window's defaults), show roots and a graph */
xmin = xx[1] - 5;
xmax = xx[2] + 5;
ymin = -20;
ymax = 20;
win = New Window( "The roots of a quadratic function",
V List Box(
Text Box( "The real roots for the equation " ),
Text Box( " " || Expr( po ) || " = 0" ),
H List Box( Text Box( "are x=" ), Text Box( xxx ) ),
Text Box( " " ), // to get a blank line
Graph Box(
Frame Size( 200, 200 ),
X Scale( xmin, xmax ),
Y Scale( ymin, ymax ),
Line Style( 2 ),
H Line( 0 ),
Line Style( 0 ),
Y Function( polynomial, x ),
Line Style( 3 ),
Pen Color( 3 ),
V Line( xx[1] ),
V Line( xx[2] ),
Marker Size( 2 ),
Marker( 0, {xx[1], 0}, {xx[2], 0} )
)
)
);
);
error = Expr(
/* if no (for example, with a=3, b=4, c=5), put up an error
window with a helpful graph */
win = New Window( "Error",
V List Box(
Text Box( " " ),
Text Box( " Polynomial " || po || " has no real roots. " ),
Text Box( " " ),
Text Box( "Examine a graph of the function to get an idea why." ),
Graph Box(
Frame Size( 200, 200 ),
X Scale( -20, 20 ),
Y Scale( -20, 20 ),
Line Style( 2 ),
H Line( 0 ),
Line Style( 0 ),
Y Function( polynomial, x )
)
)
)
);
polynomial = Expr( a * x ^ 2 + b * x + c );
// either way, the script needs to have some strings ready
// rewrite the polynomial with the coefficients specified
po = Char( Eval Expr( polynomial ) );
// store this instance of the polynomial as a string:
xxx = Char( Eval Expr( x ) );
//Store the solution list as a string
If( Is Missing( xx[1] ) | Is Missing( xx[2] ), // now it’s ready for a test
error,
results
);
Clicking OK, displays a results window (The Custom Platform’s Report, left), with either the roots or an error message. Rerun the script, input 5, 4, and 5 respectively and click OK. Note that JMP displays an error message (The Custom Platform’s Report, right).
The Custom Platform’s Report
