Subs Result Still Has Symbolic Variable In It

So as you can see from the result from the console, I am attempting to substitute all the symbolic variables in the symbolic expression tauB(1) with values. But the result of this substitution still has one of the symbolic variables that I substituted for in it? Not sure why this is or how to fix it. tauB(1) is a bit of a length expression but I'll post it here anyway.

>> tauB(1)
 
ans =
 
- (4115149222386437697*rpm1^5)/12980742146337069071326240823050240000000 + (21808513960237945171*rpm1^4)/792281625142643375935439503360000000 - (21217777204886075429*rpm1^3)/24178516392292583494123520000000 + (10349500888931238881*rpm1^2)/737869762948382064640000000 - (29738775089977568461*rpm1)/360287970189639680000000 + (4115149222386437697*rpm2^5)/12980742146337069071326240823050240000000 - (21808513960237945171*rpm2^4)/792281625142643375935439503360000000 + (21217777204886075429*rpm2^3)/24178516392292583494123520000000 - (10349500888931238881*rpm2^2)/737869762948382064640000000 + (29738775089977568461*rpm2)/360287970189639680000000 + (4115149222386437697*rpm3^5)/12980742146337069071326240823050240000000 - (21808513960237945171*rpm3^4)/792281625142643375935439503360000000 + (21217777204886075429*rpm3^3)/24178516392292583494123520000000 - (10349500888931238881*rpm3^2)/737869762948382064640000000 + (29738775089977568461*rpm3)/360287970189639680000000 - (4115149222386437697*rpm4^5)/12980742146337069071326240823050240000000 + (21808513960237945171*rpm4^4)/792281625142643375935439503360000000 - (21217777204886075429*rpm4^3)/24178516392292583494123520000000 + (10349500888931238881*rpm4^2)/737869762948382064640000000 - (29738775089977568461*rpm4)/360287970189639680000000 + w_kp
 

Any idea how to fix the subs command to get it to truly substitute for all symbolic vars?

[Walter Roberson]

Please attach tauB(1) in the form of a .mat so we can test.

When I use the expression you posted, rpm3 and rpm4 cancel out, leaving an expression with only rpm1, rpm2, and w_kp

Please also check to see whether rpm1, rpm2, rpm3, rpm4, or w_kp have been assigned values in the workspace that are different than their names. For example if after building tauB you had done

 syms x; w_kp = x

then at the time of the subs(), w_kp would have content that named a different variable, but tauB would have the original w_kp in it.

Answer 1

[madhan ravi]

change [ ] to { }

[Cory Ibanez]

Didn't work =/ I get the exact same result.

>> symvar(tauB(1))

ans =

[ rpm1, rpm2, rpm3, rpm4, w_kp]

>> subs(tauB(1), {rpm1, rpm2, rpm3, rpm4, w_kp}, {0, 20000, 20000, 0, 0})

ans =

w_kp - 203641240657422507496524617727/309485009821345068724781056000

>>

[madhan ravi]

type syms in command window and post the result

[Malte]

I would like to add another issue that I came across and which also seems to happen in the shown issue above. Why doesn't MATLAB calculate the result of the expression 203641240657422507496524617727/309485009821345068724781056000?

[Torsten]

Apply "double" to the result.

[Walter Roberson]

@Malte

sympref('FloatingPointOutput', true)