dsolve生成不一致的輸出

Question

我一直在玩這一段時間，任何人都可以解釋爲什麼我從Code1和Code2得到不同的答案？關於'dsolve（）'的實際腳本是什麼使得2個代碼的輸出不同？可以輸出，如果我只是用不同的語法相同（即」;」。「）

%Code1: 

syms Qua t Area height 

rate_in = 3*Qua*(sin(t))^2; 
delta_Vol = dsolve('DAreaY = rate_in - Qua'); 
delta_Height= dsolve('Dheight = ((rate_in - Qua)/Area)', 'height(0) = 0'); 
subfnc1 = subs(rate_in, {Qua}, {450}); 
fnc1 = subs(delta_Height, {'rate_in'}, {subfnc1}); 
fnc1 = subs(fnc1, {Area, Qua}, {1250,450}); 
fnc_main = matlabFunction(fnc1); 
fnc_main(0:10)'; 

%Code2: 

syms Qua t Area height 

rate_in = 3*Qua*(sin(t))^2; 
delta_Vol = dsolve('DAreaY = 3*Qua*(sin(t))^2 - Qua'); 
delta_Height= dsolve('Dheight = ((3*Qua*(sin(t))^2 - Qua)/Area)', 'height(0) = 0'); 
fnc1 = subs(delta_Height, {Area, Qua}, {1250,450}); 
fnc_main = matlabFunction(fnc1); 
fnc_main(0:10)'; 

是什麼樣的dsolved功能我不明白

Answer 1

這個問題可能？是你傳遞字符串dsolve而不是象徵性的表達這意味着，在第一種情況下rate_i可能被解釋爲一個常數，而不是t功能

這裏就是你可能嘗試做的。：將Dheight定義爲sym，並告知dsolve做什麼用sym S：因爲它不使用，含有不明確的參考(D)AreaY

我dsolve改變從

• 我刪除delta_Vol：

  %Code1: 
  
  clear Qua t Area height Dheight 
  syms Qua t Area height(t) Dheight 
  
  Dheight = diff(height); 
  rate_in = 3*Qua*(sin(t))^2; 
  delta_Height= dsolve(Dheight == ((rate_in - Qua)/Area), height(0) == 0); 
  subfnc1 = subs(rate_in, {Qua}, {450}); 
  fnc1 = subs(delta_Height, {'rate_in'}, {subfnc1}); 
  fnc1 = subs(fnc1, {Area, Qua}, {1250,450}); 
  fnc_main = matlabFunction(fnc1) 
  
  %Code2: 
  
  clear Qua t Area height Dheight 
  syms Qua t Area height(t) Dheight 
  
  Dheight = diff(height); 
  rate_in = 3*Qua*(sin(t))^2; 
  delta_Height= dsolve(Dheight == ((3*Qua*(sin(t))^2 - Qua)/Area), height(0) == 0); 
  fnc1 = subs(delta_Height, {Area, Qua}, {1250,450}); 
  fnc_main = matlabFunction(fnc1) 
  

  更改您的版本字符串以符號表達，同時=必須更改爲==

• 我定義了DHeight爲diff(Height)，這意味着height必須聲明爲height(t)。這也允許我們將初始條件定義爲height(0)==0，否則我們需要保留這個字符串：'height(0)=0'。

現在，這兩個版本返回相同的解決方案：

fnc_main = 

    @(t)t.*(9.0./5.0e1)-sin(t.*2.0).*(2.7e1./1.0e2) 

我建議在紙面上檢查是否該解決方案，或者其象徵前身

delta_Height = 

(Qua*(2*t - 3*sin(2*t)))/(4*Area) 

確實是你的微分方程的解決方案。