# 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

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'};
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'};
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)
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EDIT Added the integration without limits.

mohammad reza on 12 Jul 2016
ya, but not numeric integration rather symbolic'
% f = input('please input load eq \n','s'); % first input as string than convert the string to the function % make sure to put @x (variable in the input string command) % fh = str2func(f)
this takes the user defined eq ...any type...but cant integrate symbolacally
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.

mohammad reza on 12 Jul 2016
nice work it some what does the work but i need to create function handle...as i have to intregrate a user input 4 times and and each result has to be evaluated in different co ordinate values (arrays which will be also in a user defined)
but thanks for your help. i just wanted to see if there is any easy way.

#### 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'};
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))