MatLab - ODE Solver

function pushbutton39_Callback(hObject, eventdata, newHandles)
    % Get the input equation and condition from edit boxes
    edit23 = findobj(0, 'tag', 'edit23');
    edit26 = findobj(0, 'tag', 'edit26');
    eqn = get(edit23, 'String'); % Equation input
    condStr = get(edit26, 'String'); % Condition input

    % Ensure the output text field exists
    text14 = findobj(0, 'tag', 'text14');
    syms x y(x)

    % Parse the ODE input
    parsedOde = parseUserInput(eqn);

    try
        % Convert ODE to symbolic expression
        ode = str2sym(parsedOde);
    catch
        errordlg('Invalid ODE format. Please use the correct notation.', 'Error');
        return;
    end

    % Parse conditions if provided
    if isempty(condStr)
        conditions = []; % No conditions provided
    else
        try
            conditions = parseConditions(condStr);
        catch
            errordlg('Invalid conditions format. Please use the correct notation.', 'Error');
            return;
        end
    end

    % Attempt to solve the ODE with conditions
    try
        if isempty(conditions)
            % Solve without conditions
            solution = dsolve(ode);
            displayText = ['Solution (with constants): ', char(solution)];
        else
            % Solve with conditions
            solution = dsolve(ode, conditions);

            % If the solution is empty, try solving without conditions
            if isempty(solution)
                solution = dsolve(ode); % Solve without conditions
                displayText = ['Solution (with constants): ', char(solution)];
            else
                % Display the solution with conditions
                displayText = ['Solution: ', char(solution)];
            end
        end

        % Display the solution
        set(text14, 'String', displayText);
    catch ME
        % If solving fails, show error
        errordlg(['Unable to solve the ODE. ', ME.message], 'Error');
    end


function parsedConditions = parseConditions(condStr)
    % Split conditions by semicolons
    condList = split(condStr, ';');
    parsedConditions = cell(size(condList));

    syms x y(x)  % Ensure symbolic variables are defined

    for i = 1:length(condList)
        cond = strtrim(condList{i}); % Remove spaces
        if isempty(cond)
            continue; % Skip empty conditions
        end

        try
            % Prepare the condition
            if contains(cond, '=')
                parts = split(cond, '=');
                leftSide = strtrim(parts{1});  % Left side of condition
                rightSide = strtrim(parts{2}); % Right side of condition

                % Normalize condition syntax
                if contains(leftSide, '''')
                    % For derivative conditions (e.g., y' = 1)
                    cond = ['subs(diff(y(x), x), x, 0) == ', rightSide];
                else
                    % For value conditions (e.g., y(0) = 1)
                    cond = ['subs(y(x), x, 0) == ', rightSide];
                end
            end

            % Convert to symbolic form
            parsedConditions{i} = eval(cond);
        catch ME
            % If parsing fails, show error
            errordlg(['Error parsing condition: ', cond, newline, ME.message], 'Condition Parsing Error');
            parsedConditions{i} = [];
        end
    end

    % Remove empty cells and flatten
    parsedConditions = parsedConditions(~cellfun('isempty', parsedConditions));

    % Combine all conditions into a single expression
    if ~isempty(parsedConditions)
        parsedConditions = [parsedConditions{:}];
    else
        parsedConditions = [];
    end


function parsedStr = parseUserInput(userInput)
    % Replace y(5) with diff(y, x, 5)
    parsedStr = regexprep(userInput, 'y\((\d+)\)', 'diff(y, x, $1)');
    % Handle other derivatives and equality signs
    parsedStr = regexprep(parsedStr, "y''''", "diff(y, x, 4)");
    parsedStr = regexprep(parsedStr, "y'''", "diff(y, x, 3)");
    parsedStr = regexprep(parsedStr, "y''", "diff(y, x, 2)");
    parsedStr = regexprep(parsedStr, "y'", "diff(y, x)");
    parsedStr = strrep(parsedStr, "=", "=="); % Ensure equality symbol is MATLAB compatible
    parsedStr = strrep(parsedStr, 'y', 'y(x)');