Richard, First thanks for replying, I was hoping you would respond. I will try to better explain what I am attempting to do, but let me address a couple of things. 1) It is good to know that you can not go back and forth between a NESTED loop and a main loop, it is a path I have been trying to go down for a while(no pun intended) with no success. I will make the loops parallel. 2) As far as the equations matching the unknowns, while it may not be very clear, I do only have 5 unknowns for each function as for function #1 lambda is const and “a� is just a counter, and function #2 mlt is const, and again “a� is the counter. “a� is included in the solver function to load the matrix vector as each iteration is carried out, there is probably another way to do this but this seemed to be the easiest way. Loop Description: What you typed is essentially what I am trying to do. Although I would add that the values of K1 through K5 and lambda all need to be “recorded� in a matrix as it goes back and forth between Function1 and 2. Example: When Function1 is done solving, given a set of conditions, x number of vectors that are input into Matrix1, the last vector calculated acts as the initial vector to Function2 but ALSO all those values from the Function1 iteration are recorded in the same matrix as all the vectors calculated with Function2. The final output will be a matrix that has values that are a combo of values from function1 and 2. For instance “a� represents the counter and vector(each vector is the 7 values I want to see as in work sheet) position in the matrix, so say for “a� 1-250 you have Function1 values and for “a� 251-389 you have function2 values, then 390-520 function1, 521-590 function2, so on and so forth until counter reaches limit. Your questions: repeat the loop until some condition is met? Yes until the counter is finished: “a� reaches say 1440 Or are you just trying to loop through the values of Ks? No, Ks could be constant, but it is just a variable I control to manipulate the behavior of the solver functions. The number of Ks is definitely related to the total number of iterations I want the two Functions to go through, but is not controlling the loop start and stop. Does all this make sense? I can try to clarify more, and again any help is appreciated. Best, HW