Define relationship between variables in an equation

Question

ly 2021-6-19

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链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/860345-define-relationship-between-variables-in-an-equation

回答： Star Strider 2021-6-19

An equation has two variables d and t.

eqn = ((t - 21/2)*(d/2 - (20898604612049288806642049279907*t)/70957580590508366543483568128000 + 471612538725450581/36028797018963968)*(d + (20898604612049288806642049279907*t)/35478790295254183271741784064000 - 471612538725450581/18014398509481984) - ((41181014215700959230589300565923*t)/53218185442881274907612676096000 - 253280971625720775/9007199254740992)*(t/2 - 21/4)*((4992772075141567*t)/9007199254740992 - 104848213577972907/18014398509481984))/((t - 21/2)*(d + (20898604612049288806642049279907*t)/35478790295254183271741784064000 - 471612538725450581/18014398509481984) + (t/2 - 21/4)*((4992772075141567*t)/9007199254740992 - 104848213577972907/18014398509481984)) + (((41181014215700959230589300565923*t)/53218185442881274907612676096000 - 253280971625720775/9007199254740992)*(t/2 - 21/4)*((4992772075141567*t)/9007199254740992 - 104848213577972907/18014398509481984) - (t - 21/2)*(d/2 - (20898604612049288806642049279907*t)/70957580590508366543483568128000 + 471612538725450581/36028797018963968)*(d + (20898604612049288806642049279907*t)/35478790295254183271741784064000 - 471612538725450581/18014398509481984) + 39208413340930135/8796093022208)/((t - 21/2)*(d + (20898604612049288806642049279907*t)/35478790295254183271741784064000 - 471612538725450581/18014398509481984) + (t/2 - 21/4)*((4992772075141567*t)/9007199254740992 - 104848213577972907/18014398509481984) - 5373422634669521/17592186044416) == 0;

and I want to find the relationship between them like d=f(t).

How to define f(t)?

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Answer 1

Star Strider 2021-6-19

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/860345-define-relationship-between-variables-in-an-equation#answer_728455

One approach —

syms d t

eqn = ((t - 21/2)*(d/2 - (20898604612049288806642049279907*t)/70957580590508366543483568128000 + 471612538725450581/36028797018963968)*(d + (20898604612049288806642049279907*t)/35478790295254183271741784064000 - 471612538725450581/18014398509481984) - ((41181014215700959230589300565923*t)/53218185442881274907612676096000 - 253280971625720775/9007199254740992)*(t/2 - 21/4)*((4992772075141567*t)/9007199254740992 - 104848213577972907/18014398509481984))/((t - 21/2)*(d + (20898604612049288806642049279907*t)/35478790295254183271741784064000 - 471612538725450581/18014398509481984) + (t/2 - 21/4)*((4992772075141567*t)/9007199254740992 - 104848213577972907/18014398509481984)) + (((41181014215700959230589300565923*t)/53218185442881274907612676096000 - 253280971625720775/9007199254740992)*(t/2 - 21/4)*((4992772075141567*t)/9007199254740992 - 104848213577972907/18014398509481984) - (t - 21/2)*(d/2 - (20898604612049288806642049279907*t)/70957580590508366543483568128000 + 471612538725450581/36028797018963968)*(d + (20898604612049288806642049279907*t)/35478790295254183271741784064000 - 471612538725450581/18014398509481984) + 39208413340930135/8796093022208)/((t - 21/2)*(d + (20898604612049288806642049279907*t)/35478790295254183271741784064000 - 471612538725450581/18014398509481984) + (t/2 - 21/4)*((4992772075141567*t)/9007199254740992 - 104848213577972907/18014398509481984) - 5373422634669521/17592186044416) == 0;

ds = solve(eqn,d);

d(t) = vpa(ds, 5) % Define 'd(t)' As A Function Of 't'

d(t) =

figure

fplot(d, [-10 45])

grid

xlabel('t')

ylabel('d(t)')

.