All right, time now to grapple with the traction integral. So let's recall what it looks like. It is the following. It is sum over spatial dimensions. So sum now over e belonging to each of these ones, right? Of okay now and we do an integral here partial omega e t bar i w h i t bar i dS. Okay? So what that tells us is that it's really this integral that we need to consider. Okay? So we have this one Remembering that we do not have here a, a sum implied. Okay, that's straightforward. We need to do that as integral over partial omega e t bar i. For w h i, we have sum over A, NA, CA, IE. That's whi. T bar I, DS. Which is sum over A, CA ie integral partial omega E t bar I. N a, t bar i, d S. All right? And now we recall the, the cases that we've actually considered before, right? So we just need to recall them. I don't think we need to remotivate and re sort of discuss them in great detail ago, again. So the the situation that we tend to have in general is this. That is omega E. And let us consider the, the general situation where, straightaway let's consider the general situation where this face is the one of interest, right, partial omega t bar I. Okay? So what this says is that traction component i is being controlled on that surface. All right. And I've drawn it, hopefully it appears to you that it is at an angle. If that is our basis set. Okay. All right. So that is the general situation we have. Recall of course, the something we know and we have looked at before. Which is that we are somewhat saved by the fact that As I have drawn it, perhaps that one can think of that face as coming from this one. Right? So for the way I'm drawing things here, I am implying that the face of interest, is a is this face, right? It is a xi 2, xi 3 face, right? So this is partial omega xi t bar i. Sorry, t bar subscript i, for this particular element. All right? [COUGH] And so it is that we know where to con, to compute this, this integral except that we also know that when it comes to constructing our mapping, we may need to to construct local coordinates just in order to, to get the, the, the Jacobian of the mapping right. Right? So, let's suppose that in this setting, I'm calling that x delta 1. And the x delta 2 direction. Right, actually those vectors really are, e, should probably be written as e tilde 1 and e tilde 2. Anyway, those are the directions that we have, okay? And from this phase to that phase, we may think of there being a map that I denote as J sub S. Okay? C. All right? Okay. So we have all that and of course, I okay. So, so let, so, so I will, I will, I'm going to use that in a second. Before I do that, I just want to point that I also need to recall that the sum over nodes may not be over all, may not need to be over every single node, right? It may need to be only over that set of nodes. Right? And previously we've used the notation that this node, A, belongs to the set A sub n. Right? To say that that is one of the nodes corresponding to a surface with a Neumann boundary condition on it. Right? So really the sum is over A sub n, as is this one. Okay? All right, so using this map, the way we would construct this integral would be this. Now, the integral here would be over partial omega c t bar i. And for the way I've drawn it here, I am suggesting that that is C2 C3. Okay? All right. That is the, that is the C2 C3. Right? So then we have here our NA, t bar i, right? And now we're going to do the integral over dS sub C, right, which is the elemental area on the partial omega c d sub d bar i. You know, face in the bi-unit domain. And I've left some blank space here because I know that I need to construct, I know that I need to put in here determinant of js. Okay? Because js maps a surface to a surface. What is the order of js? What kind of a tensor or what kind of if you think of it as a matrix, what kind of matrix is it? Js is a 2 by 2 matrix, okay? So jS, using the notation that we've used is g l 2. Right? It maps two vectors to two vectors. Okay. It's probably useful for me to point out in addition that for the way I've constructed this particular example, dsc. It's something I stated already, but what is dsc? It is dc2, dc3. Okay? And therefore that integral would be over C2 and C3 going from minus 1 to 1, all right? Okay. So we have all of this and what we need to do is essentially go ahead and construct our vector representation of this. Okay? So in constructing the, the vector representation I'm going to write this as, now, I'm going to write this as follows. I'm going to write it as a sum A belonging to A, A sub n. Okay? Okay. And we write this as CA IE. Now that entire integral once I evaluate it, I am going to write as F. I'm going to write a T bar here,which just is reminding us that this particular type of forcing vector come to us, this particular forcing, comes to us from the traction. Okay. It is the it is an I component. Okay. And it also involved node A, okay? So that entire F with all kinds of decorations on it now with subscripts and superscripts galore, actually it has just three of them. Is the result of that integral that we carried out, right? That the integral over the surface. Okay? All right, so this is what we have. Now where does this go? Remember where this all came from. And in order to remind you of it, let me just go back to the previous slide. This is where it came from. We have at the very top of our slide here. The original integral from which this came. Right? And note, in doing this, that really there is a sum over the spatial dimensions, as the outermost sum here. Okay? And then there is the inner sum over the element integrals. Okay? So, what this is suggesting is that when it comes to assembly, okay. We will first assemble the contributions from each element. And then account for the sum over the spatial dimensions. Okay? But, but before we finally do that, there is one thing we can do which is going to get us rid of the restriction to the special set A sub N. Okay, right? And what that let's, what, what that involves is the fact that okay, so let me now say let me say the following. Mm, actually let me do one thing. Let me put a bar on this F first, okay, because what I am going to do now is just rewrite that as a sum over A, okay? Now I'm going to say that this sum runs over all the nodes in the element, CA ie, F, t bar, A, i, okay? And what I mean here is that F, t bar A i equals the F bar that I calculated on, on the line above. If A belongs to AN, right? Right, and it's equal to 0 otherwise. All right and, and you would probably recall that this was the, the approach we used when we constructed the the contribution from the Neumann boundary condition, also for the, for the scale of problem. Okay? All right. So, what have we here? We are now in a position to look at our total finite dimension you'll be performing with all these element integrals accounted for. Okay, so. [NOISE] Right? It is the following. We have sum over e. C e, so let me see, sum over e oh right, we have yeah, one more thing, yeah. We have sum over e, we also have a sum over A comma B, c, A, e transpose, right? K, AB, d, B e, okay, this is the contribution from the left hand integral, equals sum over e, sum over A, c A e transpose F internal A, okay? And plus sum over spatial dimensions. Then the sum over, elements belonging to the Neumann boundary condition corresponding to that particular spatial dimension, right? And all right. And then we have yet another sum here over A. Right? And this will over all the nodes c, a, i, e, f, t-bar, a, i. All right? Okay. Now, in writing all of these, I did notice a few minutes ago that when I introduced this matrix K, it really corresponds to a particular element, because it arose from a specific element integral, right? And it arose from the element integral for element e. So strictly speaking, I need to have it, an E there. It's just to remind us that it is the contribution from that particular element. Okay? Likewise here and likewise if there's any room here for more indices, for more subscripts. There we go. Okay. So this is where things stand. The next step that I'm going to take is one in which I am going to collapse, well not collapse actually. Expand out these vectors, okay. And in order to do that let's just let's go to a new slide.