Exclusion of inappropriate inputs in a function

In the function below the user must enter only numbers. How can I show a screen message if the user enters letters or other unwanted symbols in order to warn him that he entered an inappropriate input?

function [offsets,Nodes,lengths,angles] = grid_syr(x_i,y_i,nex,ney,L1,L2,theta,phi)

if L1 > 0 && L2 > 0 && nex > 0 && ney > 0 && mod(nex,1) == 0 && mod(ney,1) == 0 % Lengths, L1 and L2, must be positive numbers and the number of elements, nex and ney, must be positive and integers.

% Converting degrees to radians
theta = theta*pi/180; 
phi = -phi*pi/180;

L2 = L2*sin(theta); % Vertical projection of side L2

x_e = L2*cos(theta); % Extra horizontal length

Nodes      = zeros(nex*ney,4); % Initialize elements nodes' matrix
Coordinates  = zeros((nex+1)*(ney+1),2); % Initialize nodes coordinates' matrix

% Creating the nodes' matrix
for j = 1:ney
    for i = 1:nex
    
        Nodes(i+(j-1)*nex,:) = [(i+(j-1)*(nex+1)) (i+1+(j-1)*(nex+1)) (i+1+j*(nex+1)) (i+j*(nex+1))];

    end
end

rot = [cos(phi) -sin(phi);sin(phi) cos(phi)]; % Rotation matrix

% Creating the nodes coordinates' matrix
for j=1:ney+1
    for i=1:nex+1
    
        Coordinates((i+(j-1)*(nex+1)),:) = [(x_i+(j-1)*x_e+(i-1)*L1) (y_i+(j-1)*L2)]*rot;

    end
end

% Displaying the abovementioned matrices
Nodes
Coordinates

for i=1:size(Nodes,1)
    
    nexss = [(Coordinates(Nodes(i,1),1)) (Coordinates(Nodes(i,2),1)) (Coordinates(Nodes(i,3),1)) (Coordinates(Nodes(i,4),1)) (Coordinates(Nodes(i,1),1))];
    neyss = [(Coordinates(Nodes(i,1),2)) (Coordinates(Nodes(i,2),2)) (Coordinates(Nodes(i,3),2)) (Coordinates(Nodes(i,4),2)) (Coordinates(Nodes(i,1),2))];
    
    line(nexss,neyss,'Marker','.','Color','Green')
        
end

title('Grid')
xlabel('x')
ylabel('y')

for i=1:(nex+1)*(ney+1)
    
    text(Coordinates(i,1),Coordinates(i,2)+L1/20,num2str(i),'FontSize',8); % Displaying the nodes' numbers in the graph

end

 for i=1:(nex+1)*(ney+1)
    
    text(Coordinates(i,1), Coordinates(i,2)-L2/40,['(' num2str(Coordinates(i,1)) ',' num2str(Coordinates(i,2)) ')'],'FontSize',8); % Displaying the nodes' coordinates in the graph
    
end

grid on

end
end

Answer 1

[Voss]

function [offsets,Nodes,lengths,angles] = grid_syr(x_i,y_i,nex,ney,L1,L2,theta,phi)

if ~isnumeric(x_i) || ~isnumeric(y_i) ...
        || ~isnumeric(nex) || ~isnumeric(ney) ...
        || ~isnumeric(L1) || ~isnumeric(L2) ...
        || ~isnumeric(theta) || ~isnumeric(phi)
    
    uiwait(errordlg('Non-numeric input!','Error','modal'));
    
    offsets = [];
    Nodes = [];
    lengths = [];
    angles = [];
    
    return
    
end

% the rest of your function

end

[Left Terry]

Hello. It doesn't work. I called grid_syr(asdf,0,3,2,3,2,sixty,0) and it returned "Undefined function or variable 'asdf'." as an error. I don't want this.

[DGM]

Note that in your function call, you're not passing the literal text 'asdf'. You're attemptting to pass a variable named asdf. No such variable exists.

[Left Terry]

Ok, noted! If I call grid_syr('asdf',0,3,2,3,2,60,0) the function works, but I would like to exclude every case of inappropriate input. I tried ischar() and isstring() but these are not working.

[DGM]

The above does exclude those. It will exclude everything except numeric inputs.