Re: Error when using symbolic two solve for function given two points

[Doug Stewart]

On Wed, Jul 12, 2017 at 2:51 PM, RT <address@hidden> wrote:

pkg load symbolic
syms a b

assume(a, 'positive')
assume(b, 'positive')
pt1=[0,3591]  %could place all pts in one array
pt2=[66342,.01]

x1=pt1(1,1);y1=pt1(1,2)
x2=pt2(1,1);y2=pt2(1,2)

sol = solve (y1==a*b^x1, y2==a*b^x2, a, b); %creates a structure
a_val=double(sol.a) %converts structure to double
b_val=double(sol.b)

The error I get is:

warning: Using rat() heuristics for double-precision input (is this what you wanted?)
warning: called from
    sym at line 221 column 7
    binop_helper at line 54 column 5
    ineq_helper at line 35 column 5
    eq at line 53 column 5
    test_symbolic at line 28 column 5
Waiting.....................

I tried it with geogebra and it came back with an answer and a plot is this a bug?
http://storage2.static.itmages.com/i/17/0712/h_1499885162_7988333_4ba02e452b.png

I'm using symbolic 2.2.4 and Ubuntu 16.04 64bit Octave 4.0

the symbolic pkg seems to have problems solving this problem, But you don't need the symbolic

pkg for this problem. I changed some of your numbers.

pkg load symbolic

syms a b

assume(a, 'positive')

assume(b, 'positive')

pt1=[0.001,3591]  %could place all pts in one array

pt2=[.01,66342]

x1=pt1(1,1);y1=pt1(1,2);

x2=pt2(1,1);y2=pt2(1,2);

bb=(y2/y1)^(1/(x2-x1));

aa=y2/(bb^x2);

sola=solve(y2==a*bb^x2,a)

a1=double(sola)

aa

bb