Consider the boundary conditions in the wave equation solver

I solve a wave equation with Mathematica. The initial shift and speed I have already considered. However, I do not seem to be able to consider boundary conditions $ u (- pi, t) = u ( pi, t) = 0 $,

weqn = D(u(x, t), {t, 2}) == 4*D(u(x, t), {x, 2});
ic = {u(x, 0) == 0, Derivative(0, 1)(u)(x, 0) == (Sin(x))^2}
DSolveValue({weqn, ic}, u(x, t), {x, t})
Plot3D(%, {x, -Pi, Pi}, {t, 0, 4}, Mesh -> None)

I tried to write them everywhere. I always get another mistake.

Encoding Style – If-else-ladder to capture all conditions – should a redundant final clause be added?

What is missing in the answers so far depends on which type of failure is less harmful.

If your logic is good, it does not matter what you do, the important case is what happens if you have a mistake.

They omit the last condition: The last option is executed, even if this is not the right way.

You simply add the final condition: no option will be executed, depending on the situation where something may not be displayed (minor damage), or a zero reference exception may appear later (possibly debugging) pain.)

You add the last condition and an exception: it fires.

You have to decide which of these options is the best. In the development code, I think that's a snap – take the third case. However, I would probably set Circle.src to an error before throwing and circle.alt to error – if someone decides to turn off the claims later, it will harmlessly fail.

Another thing to consider – what are your recovery options? Sometimes you do not have a recovery path. What I consider the ultimate example is the first launch of the Ariane V rocket. There was an unrecognized / 0 error (actually a divisional overflow), which led to the destruction of the booster. In fact, the code that had crashed had no purpose at all at the time. Once they're in orbit or boom, you do everything to avoid mistakes. (If the missile deviates from the target for this reason, the security guard turns his key.)

Usa – Should I attend the visa date under the conditions stated below?

if really appreciate your opinion and help in this matter.

My sister has lived in the USA with her husband and child under the H1B1 visa for the last 3 years. Recently, she invited our mother to visit us.

My mother, who has applied for a visa, has gone through the document verification and the payment of the fees. She has the visa appointment this Saturday.

However, in the time between the date of the document review and the visa, my sister and brother-in-law's visa expired, and now they are returning to India. Can you tell me what we should do? Should we continue with the visa or should we postpone it? We also have other relatives in the US, but they were not mentioned in the DS-160 form.

magento2 – Add Merchant Terms & Conditions to Minicart, Cart and Checkout – Shipping Step

I'll create a payment method extension that will be displayed in the mini cart, cart, shipping and review steps on the order page.
Can I know how the merchant's terms appear below the payment button in the mini cart, shopping cart and shipping step on the order page, similar to the picture below?


How do I avoid race conditions while handling UNIX processes in C?

I am trying to create a simple UNIX shell for educational purposes. My intention is to handle background processes correctly and display a message when the job is over SIGCHLD Handler in the parent process. But my code seems to go through endlessly and create child processes whenever I attach & to my command, for example: ls &

Therefore, I assume that there are some alarming errors in terms of race conditions, as I receive my expected output when using it gdb and go into debug mode step by step, but I can not tell where I'm really wrong. Do they use the better practices for process execution? (In my original code, I made sure that jobs were processed through appropriate data structures and memory management was performed freeso that's not a problem)

Code Snippet for Reproduction: (Alternative Mirror here)


int argLength = -1;
char** argVector;
int isBackground = 0;
int childPID = -1;
int parentPID = -1;

void printPrompt()
    printf("Shell~: $ ");

char* str_concat(char* s1, char* s2)
    int l1 = strlen(s1);
    int l2 = strlen(s2);
    char* op = (char*) calloc (l1 + l2, sizeof(char));
    for(int i=0; i 0)
                        printf("(bg)  %d finishedn", pid);

                    int status;
                    waitpid(pid, NULL, WUNTRACED);
                isBackground = 0;
    return 0;

Create a view that displays a group of taxonomy conditions

I have a suggested data structure like this:


  • title
  • image
  • description
  • Taxonomy term: Campaign

campaign (Taxonomy dictionary):

I'm trying to create a view block that shows only the campaign group represented by the campaign image. The furthest thing I can do is define a relationship with the tax. Terms on the node and display all assets with that tag. I can even group them, which is exactly what I need. How do I solve the problem that "campaigns" appear as groups of assets (not the list of assets marked with this taxonomy)?

I thought I could display a list of (non-duplicate) fields in which this tax is due. Picture exists (should be once per group / aka "campaign"). But not so far ..

How do I achieve this? Have I overlooked something I am open to different approaches or ideas.

symbolic – Returns the conditions under which the variable is real

I have a complex definition of some variables (which I have used) s = Solve(1 - a x^2 - x^3 == 0, x)) and I would like to know under which conditions "a" each of the solutions will be real.

For example, one of the variables I have is r3=-(a/3) + ((1 - I Sqrt(3)) a^2)/(
3 2^(2/3) (-27 + 2 a^3 + 3 Sqrt(3) Sqrt(27 - 4 a^3))^(
1/3)) + ((1 + I Sqrt(3)) (-27 + 2 a^3 +
3 Sqrt(3) Sqrt(27 - 4 a^3))^(1/3))/(6 2^(1/3))
I want to know under what conditions r3 will be a real number.

I've tried to simplify this to the most basic example, in which I want to know what the conditions for a + b * must be in order for it to be real (where the expected answer is b = 0), and I've tried the following use Resolve(a + b I, Reals) but that does not give me the answer that I expect.

Equation Solution – Reduce, piecewise function returns a result that makes no sense under certain conditions

Here is my code:

N1 = 1;
N2 = 1;
 X1 = N2/(1 - (Sigma));

   c = 1
surpluspayoff10011010 = (N1 + x + y)/((N1 + x + y) + N2)* X1 - 
   c y - (((N1 + x)/((N1 + x) + N2))*X1);
yargmax10011010 = Simplify(y /. NSolve(!(
*SubscriptBox(((PartialD)), (y))((surpluspayoff10011010))) ==
        0, y))((2));
yargmax10011010 = 
       Reduce({Rationalize@yargmax10011010 < 0  && 0 <= (Sigma) < 1 && 
          ymax > 1}, x)}, {yargmax10011010, 
       Reduce({Rationalize@yargmax10011010 <= ymax && 
          0 <= (Sigma) < 1 && ymax > 1}, x)}, {ymax, 
       Reduce({Rationalize@yargmax10011010 > ymax && 
          0 <= (Sigma) < 1 && ymax > 1}, x)  }}));
surpluspayoff10011010 = 
  Simplify((N1 + yargmax10011010 + 
        x)/((N2) + (N1 + x + yargmax10011010))* X1 - 
    yargmax10011010 - (((N1 + x)/((N1 + x) + N2))*X1) );
yargmax10011010 = 
       Reduce({Rationalize@surpluspayoff10011010 < 0 && 
          0 <= (Sigma) < 1  && ymax > 1}, x)}, {yargmax10011010, 
       Reduce({Rationalize@surpluspayoff10011010 >= 0 && 
          0 <= (Sigma) < 1 && ymax > 1}, x)}}));

I can not state the result here because it will look very ugly here. But the thing is, I have already given the condition for 0 < sigma <1, 1 <ymax, but the result for yargmax10011010 is something that violates these conditions. Look at the result of yargmax10011010 if y = 0. We have conditions like ymax = <1 and so on

Delay sensitive database operations until additional authentication conditions are met

I have a REST API where authorized users sometimes have to make changes to their company's data. For key information (such as IBAN details may fall into this category), additional security checks must be performed before a change is actually allowed. This is to ensure that changes are not made accidentally or maliciously when an authorized user leaves their device unattended.

While we can only ask the user to enter their password as confirmation of each of these actions, this is not very flexible and we would like to allow the use of 2FA methods across the board (eg sending an email to the existing e-mail account with a confirmation URL, an OTP, etc.). In addition, we want our 2FA challenge to be available to all resources that contain sensitive information.

What is the best approach here? Some options we have considered are:

  • For each confidential collection, use an INSERT-only database table. This is very complicated to implement because we would have to replace our existing single-column primary key with compound keys, which is not really practical and means that our current REST resource IDs would have to be changed. This method also adds a significant amount to each table, which can reduce indexing.
  • Create a mirrored table for each sensitive collection. If an update occurs, it will be executed here first until a corresponding 2FA has been completed, when the resource in the main table is replaced and the temporary resource can be deleted. This method means that many of our tables are duplicates.
  • Create a table that stores confidential request data with the table it references, request processing information, and a JSON-encoded representation of the changed object. This seems to me to be the best approach, as it is easily compatible with every collection and supports all 2FAs that we will implement later. If the user authorizes, the JSON representation is copied to the correct table and the request is deleted. However, including any object representation in a column as a JSON is not in the spirit of relational databases, although I can not see that we will ever search the change request data, so this may be the most pragmatic solution.

Any thoughts on these options or better / more standard solutions?