How to terminate an if-elseif-else statement once a condition is met.

I want a situation whereby if the first 'if' statement is true (norm_sn <= del), the code should calculate x_plus and exit the if condition (jump to calculate f_x), or if the 'if' statement is false and the 'elseif' statement is true (del <= norm_s_cp), the code should calculate x_plus and exit the if statements (jump to calculate f_x). if none of the first two is true, then it can calculate the 'else'. I want it to be in that order. Can someone help me out. Thank you.

function [x_plus,grad,norm_grad,f_x,f_xplus,m_xplus] = dogleg(f,x,del)
  syms x_1 x_2 aux
  grad = subs(gradient(f,[x_1,x_2]),[x_1,x_2],x');
  norm_grad = norm(grad);
  H = subs(hessian(f,[x_1,x_2]),[x_1,x_2],x');
  %
  s_n = -H^-1*grad; norm_sn = norm(s_n);
  lambda_star1 = norm_grad^2/(grad'*H*grad);
  s_cp = -lambda_star1*grad; norm_s_cp = norm(s_cp);
  if norm_sn <= del
    x_plus = x + s_n;
  elseif del <= norm_s_cp
    x_plus = x - (del/norm_grad)*grad;
  else
    gamma = norm_grad^4/((grad'*H*grad)*(grad'*abs(s_n)));
    %gamma = norm_s_cp*norm(grad)/grad'*abs(s_n);
    eta = 0.8*gamma + 0.2;
    s_ncap = eta*s_n;
    lambda = solve(norm(s_cp + aux*(s_ncap - s_cp))^2 == del^2);
    x_plus = x + s_cp + lambda(lambda>0)*(s_ncap - s_cp);
  end
  f_x = subs(f,[x_1,x_2],x');
  f_xplus = subs(f,[x_1,x_2],x_plus');
  m_xplus = f_x + grad'*(x_plus - x) + 0.5*(x_plus - x)'*H*(x_plus - x);
end

[dpb]

Only one of the if...elseif...else...end clauses will be compute; the logical tests will be performed sequentially as written.

The possibility may exist that both the if and elseif could numerically be true as far as the logic is written since those aren't exclusive that can be ensured by inspection.

If that were possible, then only the first would ever actually happen.

If that is numerically possible, then would need to write the tests to be independent and have some other criterion to check which is the specific calculation wanted for that condition.

[Gideon Idumah]

It is actually possible for both the if and elseif to be both true. But I want a situation that if both are true, it should compute x_plus from the If statement, and exit the if...elseif...else...end loop.

[Walter Roberson]

That already happens for numeric values. And you do not have a loop.

However without knowing the f, we cannot tell whether the norm is certain to be convertible to numeric. If the norm turns out to involve symbolic variables then the comparison could invoke an error.

[Rik]

if...elseif...else...end is not a loop. If you want something to happen under some condition, make sure you have that as a test. See the example below for what happens when conditions overlap.

cond1=true;cond2=true;
if cond1 && cond2
    disp(1)
elseif cond1
    disp(2)
elseif cond2
    disp(3)
else
    disp(4)
end

Answer 1

[Image Analyst]

I don't see a loop but if there were, you could put a "break" statement there. As it is, you can put a "return" statement wherever you want to exit the function immediately, as long as all the output variables have been assigned.

[Gideon Idumah]

Thank you.

I just created a new function, and put a return at the end of the "if" and "elseif" statement.