ACCEPTED SOLUTION
Accepted Solutions
And if your equations are always linear, you could use lsolve (no initial guesses required):
Alan
Werner Exinger wrote:
How would you use that last version to get a result?
Like this?
For example:
Alan
Werner Exinger wrote:
... I was thinking of the symbolic solution to compare with the symbolic solve. Don't think we can get it that easy with the solve block set up that way as MC can't determine the dimensíons of the vectors.
Correct. I'm afraid I was only thinking of the numerical approach. I had the "solve" version in mind for the symbolic approach.
Both numeric and symbolic approaches work ok if the system is reformulated to work with lsolve:
(The last assignment also works ok if the vector of components on the LHS is simply replaced by s)
Alan
You need to supply initial guesses for a and b - see attached.
... or use the symbolic evaluation directly after the "find"
Is it simply a quirk of Mathcad or is there a logical explanation of rule for this?
The latter. An assignment will be affected by the most rightmost expression of the RHS of the assignment if there are some inline evaluations. Look at the example below. To show the difference PI had to be evaluated symbolically as we wouldn't see any difference by numeric evaluation:
In case of the solve block the assignment without the symbolic eval assigns the whole solve block to the function sol(). So every call of sol() evaluates the whole solve block again. This means that evaluating numerically using the normal = sign uses the numerical approx algorithms and requires guess values (and as you don't provide any your sheet fails here). But if you evaluate symbolically different algorithms are chosen which do not require any guess values and so you see a result in your sheet.
The added symbolic eval changes this behaviour as now sol() is not assigned the solve block but rather the result of the symbolic eval which is the 2x1-vector in c and d. Of course this vector can be evaluated numerically, too, without the need of guess values, as long as you provide numeric values for c and d.
This method works only if the solve block can be evaluated symbolically to a simple symbolic expression which may not be the case for some more complex tasks.
