MATLAB: Help with quadriatic formula

qadratic solver

Hi everyone,

We are to create a function using the editor to solve a quadratic formula. The hard part is the user is to be able to input just the equation ie: Ax^2+Bx+C=0 (not the values of ABC). (Below is what I have so far)

____***_*%The user input the formula they want solved_____
    function [xpos, xneg] = Roots(equation)
    %Quadratic equation format is = Ax^2 + Bx + C = 0
    A = strtok(equation, 'x');
    B = 
    C = 
    %This is the discriminant
    D = B .^2 - 4 .* A .* C;
    %These are the equation to find the positive and negative values of x
    xpos = (-B + sqrt(D)) ./ (2 .* A)
    xneg = (-B - sqrt(D)) ./ (2 .* A)
    end

Best Answer

You showed enough I'll do more than normally would on first response...

s=inputdlg('Enter quadratic: ','Quadratic Solver Input',1,{'ax^2+bx+c'});

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MATLAB: Quadratic equation & Minus B

The following example code snippet works for accepting the coefficients a,b and c and calculating the roots and finding if they are real or not:

a1 = 'Enter value of a ';
a = input(a1)
b1= 'Enter value of b ';
b = input(b1)
c1= 'Enter value of c ';
c = input(c1)
x1 = (-b + sqrt(b^2 - (4 * a * c))) / (2 * a);
x2 = (-b - sqrt(b^2 - (4 * a * c))) / (2 * a);
t1=isreal(x1);
t2=isreal(x2);

MATLAB: Offset of ticks labels

Not w/o using text instead of letting the axis tick property control them, no.

First fix the formatting issue with tick labels that I've harped on for nearly 30 years -- that of not putting the same number of decimal places on all labels instead of letting integers default. That may fix the problem adequately that you can live with it, but it will certainly go a long way towards the "truly professional" look that I agree is somewhat lacking as default...

ytk=get(gca,'ytick').';  % get the tick values as column vector
set(gca,'yticklabel',num2str(ytk,'%0.1f'))

Ohhh....just thought of a "trick"...let's see--

set(gca,'yticklabel',num2str(ytk,'%0.1f '))

Drat! The renderer strips out the trailing blank so only way to reposition will be via the use of text as mentioned above. Changing positions won't help as the axes labels will just move around together.

ERRATUM While this is quite old, OP did an edit that came up as new activity and in rereading the thread I notice a misstatement that just by chance I discovered the issue in just within the last couple of days at the newsgroup. That is I presumed above that the problem w/ the trailing space in the above was owing to HG; turns out it's a "feature" (I think I think it's a bug, but it's documented behavior) in num2str that it strips blanks even if given a specific format statement so the above doesn't actually pass the string with the trailing blank had assumed it did. One would have to build the string array and append the blank or use sprintf to make the format "stick". END ERRATUM

Oh, I guess you could get more complicated and add a second axes object for the actual display and set the tick labels to empty on the original...but I think just writing text is probably simpler than that.

ADDENDUM

text example code--as above start with retrieving the current tick values, then

set(gca,'yticklab',[])     % clear the labels so don't show
xtik=get(gca,'xtick'); dxtik=xtik(2)-xtik(1);  % diff between x ticks
xpos=xtik(1)-0.1*dxtik;      % a guess at suitable x location
text(repmat(xpos,size(ytk)),ytk,num2str(ytk,'%0.1f'),'horizontal','right')

The x-position is arbitrary; adjust as desired. I took 10% of the x-axis tick spacing to the left of the first x-tick. You could switch over to absolute positions and remove the dependence on the actual axes values; I'll leave that as "exercise for the student"... :)

Best Answer

Related Solutions

MATLAB: Quadratic equation & Minus B

MATLAB: Offset of ticks labels

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