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A difficulty in understanding the n-dimensional second order derivative.



The Next CEO of Stack OverflowA difficulty in understanding the proof of completeness of $l_2$.Difficulty (2) in understanding thm4.2 in Israel Gohberg.A difficulty in understanding Theorem 4.3 in Israel Gohberg.A difficulty in understanding the Gram determinant.A difficulty in understanding a part of a solution of 4.4.4 PetovicA difficulty in understanding a proof for L'Hospital's rule (in Petrovic)A difficulty in understanding a step in a solution.A difficulty in understanding a statement in example 10.6.6 Petrovic.A difficulty in understanding theorem 10.6.7 in Petrovic.(n-dimensional intermediate value theorem)A difficulty in understanding the definition of “Spaces of Matrix Elements.”










0












$begingroup$


The example and its solution is given below:




enter image description here



enter image description here




But I do not understand why in the calculation of $D^2 f(2,3)(u)^2$ the $u^2$ takes this form ....$ u_1^2 + u_1u_2 + u_2^2$ from where the term $u_1u_2$ comes?...... could anyone explain this for me please?



Edit:
I remember that my professor said that the dot product in two dimensional is just the square of the term but I do not understand this statement..... but I do not understand this statement.










share|cite|improve this question











$endgroup$







  • 1




    $begingroup$
    What is this from??
    $endgroup$
    – Randall
    Mar 18 at 12:49










  • $begingroup$
    $ u_1^2 + u_1u_2 + u_2^2$ @Randall from where the term $u_1u_2$ comes?
    $endgroup$
    – hopefully
    Mar 18 at 12:51










  • $begingroup$
    No, the book/notes.
    $endgroup$
    – Randall
    Mar 18 at 12:52










  • $begingroup$
    Petrovic "Advanced calculus theory and practice" @Randall
    $endgroup$
    – hopefully
    Mar 18 at 12:54










  • $begingroup$
    I remember that my professor said that the dot product in two dimensional is just the square of the term but I do not understand this statement.@Randall
    $endgroup$
    – hopefully
    Mar 18 at 13:01















0












$begingroup$


The example and its solution is given below:




enter image description here



enter image description here




But I do not understand why in the calculation of $D^2 f(2,3)(u)^2$ the $u^2$ takes this form ....$ u_1^2 + u_1u_2 + u_2^2$ from where the term $u_1u_2$ comes?...... could anyone explain this for me please?



Edit:
I remember that my professor said that the dot product in two dimensional is just the square of the term but I do not understand this statement..... but I do not understand this statement.










share|cite|improve this question











$endgroup$







  • 1




    $begingroup$
    What is this from??
    $endgroup$
    – Randall
    Mar 18 at 12:49










  • $begingroup$
    $ u_1^2 + u_1u_2 + u_2^2$ @Randall from where the term $u_1u_2$ comes?
    $endgroup$
    – hopefully
    Mar 18 at 12:51










  • $begingroup$
    No, the book/notes.
    $endgroup$
    – Randall
    Mar 18 at 12:52










  • $begingroup$
    Petrovic "Advanced calculus theory and practice" @Randall
    $endgroup$
    – hopefully
    Mar 18 at 12:54










  • $begingroup$
    I remember that my professor said that the dot product in two dimensional is just the square of the term but I do not understand this statement.@Randall
    $endgroup$
    – hopefully
    Mar 18 at 13:01













0












0








0





$begingroup$


The example and its solution is given below:




enter image description here



enter image description here




But I do not understand why in the calculation of $D^2 f(2,3)(u)^2$ the $u^2$ takes this form ....$ u_1^2 + u_1u_2 + u_2^2$ from where the term $u_1u_2$ comes?...... could anyone explain this for me please?



Edit:
I remember that my professor said that the dot product in two dimensional is just the square of the term but I do not understand this statement..... but I do not understand this statement.










share|cite|improve this question











$endgroup$




The example and its solution is given below:




enter image description here



enter image description here




But I do not understand why in the calculation of $D^2 f(2,3)(u)^2$ the $u^2$ takes this form ....$ u_1^2 + u_1u_2 + u_2^2$ from where the term $u_1u_2$ comes?...... could anyone explain this for me please?



Edit:
I remember that my professor said that the dot product in two dimensional is just the square of the term but I do not understand this statement..... but I do not understand this statement.







real-analysis calculus linear-algebra analysis multivariable-calculus






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Mar 18 at 13:02







hopefully

















asked Mar 18 at 12:48









hopefullyhopefully

277214




277214







  • 1




    $begingroup$
    What is this from??
    $endgroup$
    – Randall
    Mar 18 at 12:49










  • $begingroup$
    $ u_1^2 + u_1u_2 + u_2^2$ @Randall from where the term $u_1u_2$ comes?
    $endgroup$
    – hopefully
    Mar 18 at 12:51










  • $begingroup$
    No, the book/notes.
    $endgroup$
    – Randall
    Mar 18 at 12:52










  • $begingroup$
    Petrovic "Advanced calculus theory and practice" @Randall
    $endgroup$
    – hopefully
    Mar 18 at 12:54










  • $begingroup$
    I remember that my professor said that the dot product in two dimensional is just the square of the term but I do not understand this statement.@Randall
    $endgroup$
    – hopefully
    Mar 18 at 13:01












  • 1




    $begingroup$
    What is this from??
    $endgroup$
    – Randall
    Mar 18 at 12:49










  • $begingroup$
    $ u_1^2 + u_1u_2 + u_2^2$ @Randall from where the term $u_1u_2$ comes?
    $endgroup$
    – hopefully
    Mar 18 at 12:51










  • $begingroup$
    No, the book/notes.
    $endgroup$
    – Randall
    Mar 18 at 12:52










  • $begingroup$
    Petrovic "Advanced calculus theory and practice" @Randall
    $endgroup$
    – hopefully
    Mar 18 at 12:54










  • $begingroup$
    I remember that my professor said that the dot product in two dimensional is just the square of the term but I do not understand this statement.@Randall
    $endgroup$
    – hopefully
    Mar 18 at 13:01







1




1




$begingroup$
What is this from??
$endgroup$
– Randall
Mar 18 at 12:49




$begingroup$
What is this from??
$endgroup$
– Randall
Mar 18 at 12:49












$begingroup$
$ u_1^2 + u_1u_2 + u_2^2$ @Randall from where the term $u_1u_2$ comes?
$endgroup$
– hopefully
Mar 18 at 12:51




$begingroup$
$ u_1^2 + u_1u_2 + u_2^2$ @Randall from where the term $u_1u_2$ comes?
$endgroup$
– hopefully
Mar 18 at 12:51












$begingroup$
No, the book/notes.
$endgroup$
– Randall
Mar 18 at 12:52




$begingroup$
No, the book/notes.
$endgroup$
– Randall
Mar 18 at 12:52












$begingroup$
Petrovic "Advanced calculus theory and practice" @Randall
$endgroup$
– hopefully
Mar 18 at 12:54




$begingroup$
Petrovic "Advanced calculus theory and practice" @Randall
$endgroup$
– hopefully
Mar 18 at 12:54












$begingroup$
I remember that my professor said that the dot product in two dimensional is just the square of the term but I do not understand this statement.@Randall
$endgroup$
– hopefully
Mar 18 at 13:01




$begingroup$
I remember that my professor said that the dot product in two dimensional is just the square of the term but I do not understand this statement.@Randall
$endgroup$
– hopefully
Mar 18 at 13:01










1 Answer
1






active

oldest

votes


















1












$begingroup$

The object $q:=D^2f(2,3)$ is a quadratic form in the increment variable $bf u=(u_1,u_2)$. The vector $bf u$ is attached at the point $bf p=(2,3)inrm dom(f)$, in other words: $bf u$ is a vector in the tangent space $T_bf p$. One has
$$q(bf u)=sum_i, >k=1^2 f_.ik(bf p)>u_iu_k=[u_1 u_2]left[matrix-6&6cr 6&30crright]left[matrixu_1cr u_2crright]=-6u_1^2+12u_1u_2+30 u_2^2 .$$






share|cite|improve this answer











$endgroup$












  • $begingroup$
    what is $T_p$?
    $endgroup$
    – hopefully
    Mar 18 at 13:12











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1 Answer
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active

oldest

votes








1 Answer
1






active

oldest

votes









active

oldest

votes






active

oldest

votes









1












$begingroup$

The object $q:=D^2f(2,3)$ is a quadratic form in the increment variable $bf u=(u_1,u_2)$. The vector $bf u$ is attached at the point $bf p=(2,3)inrm dom(f)$, in other words: $bf u$ is a vector in the tangent space $T_bf p$. One has
$$q(bf u)=sum_i, >k=1^2 f_.ik(bf p)>u_iu_k=[u_1 u_2]left[matrix-6&6cr 6&30crright]left[matrixu_1cr u_2crright]=-6u_1^2+12u_1u_2+30 u_2^2 .$$






share|cite|improve this answer











$endgroup$












  • $begingroup$
    what is $T_p$?
    $endgroup$
    – hopefully
    Mar 18 at 13:12















1












$begingroup$

The object $q:=D^2f(2,3)$ is a quadratic form in the increment variable $bf u=(u_1,u_2)$. The vector $bf u$ is attached at the point $bf p=(2,3)inrm dom(f)$, in other words: $bf u$ is a vector in the tangent space $T_bf p$. One has
$$q(bf u)=sum_i, >k=1^2 f_.ik(bf p)>u_iu_k=[u_1 u_2]left[matrix-6&6cr 6&30crright]left[matrixu_1cr u_2crright]=-6u_1^2+12u_1u_2+30 u_2^2 .$$






share|cite|improve this answer











$endgroup$












  • $begingroup$
    what is $T_p$?
    $endgroup$
    – hopefully
    Mar 18 at 13:12













1












1








1





$begingroup$

The object $q:=D^2f(2,3)$ is a quadratic form in the increment variable $bf u=(u_1,u_2)$. The vector $bf u$ is attached at the point $bf p=(2,3)inrm dom(f)$, in other words: $bf u$ is a vector in the tangent space $T_bf p$. One has
$$q(bf u)=sum_i, >k=1^2 f_.ik(bf p)>u_iu_k=[u_1 u_2]left[matrix-6&6cr 6&30crright]left[matrixu_1cr u_2crright]=-6u_1^2+12u_1u_2+30 u_2^2 .$$






share|cite|improve this answer











$endgroup$



The object $q:=D^2f(2,3)$ is a quadratic form in the increment variable $bf u=(u_1,u_2)$. The vector $bf u$ is attached at the point $bf p=(2,3)inrm dom(f)$, in other words: $bf u$ is a vector in the tangent space $T_bf p$. One has
$$q(bf u)=sum_i, >k=1^2 f_.ik(bf p)>u_iu_k=[u_1 u_2]left[matrix-6&6cr 6&30crright]left[matrixu_1cr u_2crright]=-6u_1^2+12u_1u_2+30 u_2^2 .$$







share|cite|improve this answer














share|cite|improve this answer



share|cite|improve this answer








edited Mar 18 at 13:41

























answered Mar 18 at 13:10









Christian BlatterChristian Blatter

175k8115327




175k8115327











  • $begingroup$
    what is $T_p$?
    $endgroup$
    – hopefully
    Mar 18 at 13:12
















  • $begingroup$
    what is $T_p$?
    $endgroup$
    – hopefully
    Mar 18 at 13:12















$begingroup$
what is $T_p$?
$endgroup$
– hopefully
Mar 18 at 13:12




$begingroup$
what is $T_p$?
$endgroup$
– hopefully
Mar 18 at 13:12

















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