On Wed, Sep 7, 2011 at 7:31 PM, Chipslinger <cbol...@boltoneng.com> wrote:
> I've been messing around with using Sage for solving node equations. I
> have the right syntax and structure for creating and symbolically
> solving equations, but am struggling with:
> * Using solve in a loop -- it doesn't evaluate using new
> parameters each time through
> * Printing in decimal format -- I've tried using N(x, digits=4),
> but can't get it to work with the result from solve; I get lots of
> errors
>
> Here's a simple program I tried last night (using sagenb.org version
> 4.7):
>
> # Schmitt Trigger Threshold Calculation
> var('rtop, rbot, rfd, rout_pullup, vnode, vcc, vin, vthresh')
> rtop = 10000
> rbot = 10000
> rout_pullup = 10000
> rfd = 1e6
> vin = 5
> #vcc = 5
> eq1 = (vin-vnode)/rtop + (vcc-vnode)/(rout_pullup+rfd) == vnode/rbot
> out_states = [0, 5]
> for i in range(2):
> vcc = out_states[i]
> vthresh = solve([eq1], vnode)
> print '%4s: %4s'%(vcc, vthresh)
>
> Any help or pointers towards relevant docs would be greatly
> appreciated. Thank you in advance.
>
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How about this -
# Schmitt Trigger Threshold Calculation
var('rtop, rbot, rfd, rout_pullup, vnode, vcc, vin, vthresh')
rtop = 10000
rbot = 10000
rout_pullup = 10000
rfd = 1e6
vin = 5
#vcc = 5
eq1 = (vin-vnode)/rtop + (vcc-vnode)/(rout_pullup+rfd) == vnode/rbot
out_states = [0, 5]
vthresh = solve([eq1], vnode)[0].rhs()
for i in range(2):
vcc = out_states[i]
print '%4s: %.4f'%(vcc, vthresh.substitute(vcc=vcc).n())
output is -
0: 2.4877
5: 2.5123
I have done very small changes in your code. Hope it helps.
Rajeev
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