integrating input variable function

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

Answer 1

[Star Strider]

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)

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EDIT — Added the integration without limits.

[mohammad reza]

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]

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.

Answer 2

[mohammad reza]

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.

[Star Strider]

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