integrating input variable function
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mohammad reza
on 12 Jul 2016
Commented: Star Strider
on 12 Jul 2016
how can i input a user defined variable/ quadratic equation and integrate it?
what i am trying to do is ask user for the equation in then integrate it, (no limit) and give the ans
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Accepted Answer
Star Strider
on 12 Jul 2016
Edited: Star Strider
on 12 Jul 2016
This is how I would do it:
Integrating the quadratic without integration limits and displaying the result:
prompt = {'x^2 Coefficient', 'x Coefficient', 'Constant'};
default_ans = {'0','0','0'};
dlg_title = 'Quadratic Equation';
num_lines = 1;
valc = inputdlg(prompt, dlg_title, num_lines, default_ans);
vals = cell2mat(valc);
valn = str2num(vals);
qcf = valn(1:3);
qint = polyint(qcf.');
CreateStruct.Interpreter = 'tex';
CreateStruct.WindowStyle = 'modal';
msgbox(sprintf('Integral of: \n%.2f\\cdotx^2 %+.2f\\cdotx %+.2f = \n%.2f\\cdotx^3 %+.2f\\cdotx^2 %+.2f\\cdotx %+.2f', [qcf.' qint]),'Value',CreateStruct)
Integrating the quadratic with limits and displaying the results of the integration:
prompt = {'x^2 Coefficient', 'x Coefficient', 'Constant', 'Lower Integration Limit','Upper Integration Limit'};
default_ans = {'0','0','0','0','0'};
dlg_title = 'Quadratic Equation';
num_lines = 1;
valc = inputdlg(prompt, dlg_title, num_lines, default_ans);
vals = cell2mat(valc);
valn = str2num(vals);
qcf = valn(1:3);
int_lim = valn(4:5);
qint = polyint(qcf.');
int_val = diff(polyval(qint, [int_lim(1),int_lim(2)]));
CreateStruct.Interpreter = 'tex';
CreateStruct.WindowStyle = 'modal';
msgbox(sprintf('Integral of %.2f\\cdotx^2 %+.2f\\cdotx %+.2f from %.2f to %.2f = %.3f', [qcf.' int_lim.' int_val]),'Value',CreateStruct)
----------
EDIT — Added the integration without limits.
2 Comments
Star Strider
on 12 Jul 2016
We were typing at the same time.
I re-read your question and added a section that calculates the symbolic integral of the quadratic and displays the integrated result, without actually integrating it. This code does not create a function handle, but that is relatively easy to do if you need to.
More Answers (1)
mohammad reza
on 12 Jul 2016
1 Comment
Star Strider
on 12 Jul 2016
To create a funciton handle, add str2func and sprintf calls:
prompt = {'x^2 Coefficient', 'x Coefficient', 'Constant'};
default_ans = {'0','0','0'};
dlg_title = 'Quadratic Equation';
num_lines = 1;
valc = inputdlg(prompt, dlg_title, num_lines, default_ans);
vals = cell2mat(valc);
valn = str2num(vals);
qcf = valn(1:3);
qint = polyint(qcf.');
intquad_fcn = str2func(sprintf('@(x) %f.*x.^3 + %f.*x.^2 + %f.*x + %f', qint))
intquad_fcn =
@(x)0.333333.*x.^3+1.000000.*x.^2+3.000000.*x+0.000000
It exists as the function in the code, so adding one line to test it:
intquad_val = intquad_fcn(5) % Test Line (Delete Later)
intquad_val =
81.6666e+000
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