Need assistance error im getting from GUI

    function varargout = diffyQ(varargin)

% DIFFYQ MATLAB code for diffyQ.fig

%      DIFFYQ, by itself, creates a new DIFFYQ or raises the existing

%      singleton*.

%

%      H = DIFFYQ returns the handle to a new DIFFYQ or the handle to
%      the existing singleton*.

%

%      DIFFYQ('CALLBACK',hObject,eventData,handles,...) calls the local

%      function named CALLBACK in DIFFYQ.M with the given input arguments.
%

%      DIFFYQ('Property','Value',...) creates a new DIFFYQ or raises the

%      existing singleton*.  Starting from the left, property value pairs are

%      applied to the GUI before diffyQ_OpeningFcn gets called.  An

%      unrecognized property name or invalid value makes property application

%      stop.  All inputs are passed to diffyQ_OpeningFcn via varargin.
%

%      *See GUI Options on GUIDE's Tools menu.  Choose "GUI allows only one

%      instance to run (singleton)".
%

% See also: GUIDE, GUIDATA, GUIHANDLES

% Edit the above text to modify the response to help diffyQ

% Last Modified by GUIDE v2.5 12-Apr-2018 12:08:25

% Begin initialization code - DO NOT EDIT

gui_Singleton = 1;

gui_State = struct('gui_Name',       mfilename, ...
                   'gui_Singleton',  gui_Singleton, ...
                   'gui_OpeningFcn', @diffyQ_OpeningFcn, ...
                   'gui_OutputFcn',  @diffyQ_OutputFcn, ...
                   'gui_LayoutFcn',  [] , ...
                   'gui_Callback',   []);
if nargin && ischar(varargin{1})
    gui_State.gui_Callback = str2func(varargin{1});
end

if nargout
    [varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});
else
    gui_mainfcn(gui_State, varargin{:});
end

% End initialization code - DO NOT EDIT

% --- Executes just before diffyQ is made visible.

function diffyQ_OpeningFcn(hObject, eventdata, handles, varargin)

% This function has no output args, see OutputFcn.

% hObject    handle to figure

% eventdata  reserved - to be defined in a future version of MATLAB

% handles    structure with handles and user data (see GUIDATA)

% varargin   command line arguments to diffyQ (see VARARGIN)

% Choose default command line output for diffyQ

handles.output = hObject;

% Update handles structure

guidata(hObject, handles);

% UIWAIT makes diffyQ wait for user response (see UIRESUME)

% uiwait(handles.figure1);

% --- Outputs from this function are returned to the command line.

function varargout = diffyQ_OutputFcn(hObject, eventdata, handles) 

% varargout  cell array for returning output args (see VARARGOUT);

% hObject    handle to figure

% eventdata  reserved - to be defined in a future version of MATLAB

% handles    structure with handles and user data (see GUIDATA)

% Get default command line output from handles structure

varargout{1} = handles.output;

function input_Callback(hObject, eventdata, handles)

% hObject    handle to input (see GCBO)

% eventdata  reserved - to be defined in a future version of MATLAB

% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of input as text

%        str2double(get(hObject,'String')) returns contents of input as a double

% --- Executes during object creation, after setting all properties.

function input_CreateFcn(hObject, eventdata, handles)

% hObject    handle to input (see GCBO)

% eventdata  reserved - to be defined in a future version of MATLAB

% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.

%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end

% --- Executes on button press in pushbutton1.
function pushbutton1_Callback(hObject, eventdata, handles)

% hObject    handle to pushbutton1 (see GCBO)

% eventdata  reserved - to be defined in a future version of MATLAB

% handles    structure with handles and user data (see GUIDATA)

diffyEQ = solution(x1);
set(handles.solution, 'String', char(diffyEQ));

   function diffyEQ=solution(x1)

syms t y(t)

x1=10*exp(-3*t)

x=diff(x1)

Dy = diff(y);

D2y = diff(y,2);

diffyEQ = dsolve(D2y+3*Dy+2*y == x, y(0) == 0, Dy(0) == -5)

Here are my errors

Undefined function or variable 'x1'.

Error in diffyQ>pushbutton1_Callback (line 103)

diffyEQ = solution(x1);

Error in gui_mainfcn (line 95)

          feval(varargin{:});

Error in diffyQ (line 42)

      gui_mainfcn(gui_State, varargin{:});

Error in

matlab.graphics.internal.figfile.FigFile/read>@(hObject,eventdata)diffyQ('pushbutton1_Callback',hObject,eventdata,guidata(hObject)) 

Error while evaluating UIControl Callback.

Answer 1

[Walter Roberson]

You are calling

 diffyEQ = solution(x1);

when you have not assigned anything to x1.

However it is not clear why you are bothering to pass anything to solution(), since inside that routine you have

x1=10*exp(-3*t)

which would overwrite whatever parameter was passed anyhow.